diff --git a/flang-rt/unittests/CMakeLists.txt b/flang-rt/unittests/CMakeLists.txt
index 53cd54dfd215e..e1ab73d7d9301 100644
--- a/flang-rt/unittests/CMakeLists.txt
+++ b/flang-rt/unittests/CMakeLists.txt
@@ -22,12 +22,8 @@ if (CMAKE_CROSSCOMPILING)
   return ()
 endif ()
 
-if (NOT TARGET llvm_gtest)
-  message(WARNING "Flang-RT unittests disabled due to GTest being unavailable; "
-                  "Try LLVM_INSTALL_GTEST=ON for the LLVM build")
-  return ()
-endif ()
-
+# Make the targets default_gtest and default_gtest_main available.
+build_gtest()
 
 add_dependencies(flang-rt-test-depends
   FlangRTUnitTests
diff --git a/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp b/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
index 8c0a6f29b6967..1a9817cc665de 100644
--- a/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
+++ b/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
@@ -9,7 +9,6 @@
 #include "flang-rt/runtime/descriptor.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Testing/testing.h"
-#include "llvm/Support/raw_ostream.h"
 #include <type_traits>
 
 using namespace Fortran::runtime;
@@ -73,26 +72,9 @@ static void AddNoiseToCdesc(CFI_cdesc_t *dv, CFI_rank_t rank) {
   }
 }
 
-#ifdef VERBOSE
-static void DumpTestWorld(const void *bAddr, CFI_attribute_t attr,
-    CFI_type_t ty, std::size_t eLen, CFI_rank_t rank,
-    const CFI_index_t *eAddr) {
-  llvm::outs() << " base_addr: ";
-  llvm::outs().write_hex(reinterpret_cast<std::intptr_t>(bAddr))
-      << " attribute: " << static_cast<int>(attr)
-      << " type: " << static_cast<int>(ty) << " elem_len: " << eLen
-      << " rank: " << static_cast<int>(rank) << " extent: ";
-  llvm::outs().write_hex(reinterpret_cast<std::intptr_t>(eAddr)) << '\n';
-  llvm::outs().flush();
-}
-#endif
-
 static void check_CFI_establish(CFI_cdesc_t *dv, void *base_addr,
     CFI_attribute_t attribute, CFI_type_t type, std::size_t elem_len,
     CFI_rank_t rank, const CFI_index_t extents[]) {
-#ifdef VERBOSE
-  DumpTestWorld(base_addr, attribute, type, elem_len, rank, extent);
-#endif
   // CFI_establish reqs from F2018 section 18.5.5
   int retCode{
       CFI_establish(dv, base_addr, attribute, type, elem_len, rank, extents)};
@@ -305,9 +287,6 @@ static void check_CFI_allocate(CFI_cdesc_t *dv,
   const CFI_type_t type{dv->type};
   const void *base_addr{dv->base_addr};
   const int version{dv->version};
-#ifdef VERBOSE
-  DumpTestWorld(base_addr, attribute, type, elem_len, rank, nullptr);
-#endif
   int retCode{CFI_allocate(dv, lower_bounds, upper_bounds, elem_len)};
   Descriptor *desc = reinterpret_cast<Descriptor *>(dv);
   if (retCode == CFI_SUCCESS) {
diff --git a/flang-rt/unittests/Runtime/AccessTest.cpp b/flang-rt/unittests/Runtime/AccessTest.cpp
index d431d0d19bd61..d44f0ec3ced23 100644
--- a/flang-rt/unittests/Runtime/AccessTest.cpp
+++ b/flang-rt/unittests/Runtime/AccessTest.cpp
@@ -12,8 +12,8 @@
 #include "CrashHandlerFixture.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/extensions.h"
-#include "llvm/ADT/Twine.h"
 
+#include <cstring>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -82,8 +82,9 @@ static const char *temp_directory_path() {
 
 static std::string createTemporaryFile(
     const char *name, const AccessType &accessType) {
-  std::string path =
-      (llvm::Twine{temp_directory_path()} + "/" + addPIDSuffix(name)).str();
+  std::ostringstream pathS;
+  pathS << temp_directory_path() << "/" << addPIDSuffix(name);
+  std::string path = pathS.str();
 
   // O_CREAT | O_EXCL enforces that this file is newly created by this call.
   // This feels risky. If we don't have permission to create files in the
diff --git a/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp b/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
index 8213edd1f9225..34901b5cd2139 100644
--- a/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
+++ b/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
@@ -17,12 +17,11 @@
   char buffer[1000];
   std::vsnprintf(buffer, sizeof buffer, message, ap);
   va_end(ap);
-  llvm::errs()
-      << "Test "
-      << ::testing::UnitTest::GetInstance()->current_test_info()->name()
-      << " crashed in file "
-      << (sourceFile ? sourceFile : "unknown source file") << '(' << sourceLine
-      << "): " << buffer << '\n';
+  std::cerr << "Test "
+            << ::testing::UnitTest::GetInstance()->current_test_info()->name()
+            << " crashed in file "
+            << (sourceFile ? sourceFile : "unknown source file") << '('
+            << sourceLine << "): " << buffer << '\n';
   std::exit(EXIT_FAILURE);
 }
 
diff --git a/flang-rt/unittests/Runtime/Descriptor.cpp b/flang-rt/unittests/Runtime/Descriptor.cpp
index 3a4a7670fc62e..4a7bb43a492af 100644
--- a/flang-rt/unittests/Runtime/Descriptor.cpp
+++ b/flang-rt/unittests/Runtime/Descriptor.cpp
@@ -32,8 +32,8 @@ TEST(Descriptor, FixedStride) {
   extent[0] = 8;
   descriptor.Establish(integer, four, data, 1, extent);
   ASSERT_EQ(descriptor.rank(), 1);
-  ASSERT_EQ(descriptor.Elements(), 8);
-  ASSERT_EQ(descriptor.ElementBytes(), four);
+  ASSERT_EQ(descriptor.Elements(), 8u);
+  ASSERT_EQ(descriptor.ElementBytes(), static_cast<unsigned>(four));
   ASSERT_EQ(descriptor.GetDimension(0).LowerBound(), 0);
   ASSERT_EQ(descriptor.GetDimension(0).ByteStride(), four);
   ASSERT_EQ(descriptor.GetDimension(0).Extent(), 8);
diff --git a/flang-rt/unittests/Runtime/ExternalIOTest.cpp b/flang-rt/unittests/Runtime/ExternalIOTest.cpp
index 6c148b1de6f82..6421194f45141 100644
--- a/flang-rt/unittests/Runtime/ExternalIOTest.cpp
+++ b/flang-rt/unittests/Runtime/ExternalIOTest.cpp
@@ -16,7 +16,6 @@
 #include "flang/Runtime/io-api.h"
 #include "flang/Runtime/main.h"
 #include "flang/Runtime/stop.h"
-#include "llvm/Support/raw_ostream.h"
 #include <cstring>
 #include <string_view>
 
diff --git a/libc/benchmarks/CMakeLists.txt b/libc/benchmarks/CMakeLists.txt
index 60f522d7d8c65..c17cc106f96d7 100644
--- a/libc/benchmarks/CMakeLists.txt
+++ b/libc/benchmarks/CMakeLists.txt
@@ -19,6 +19,8 @@ set(LLVM_LINK_COMPONENTS
 # Add Unit Testing Support
 #==============================================================================
 
+make_gtest_target()
+
 function(add_libc_benchmark_unittest target_name)
   if(NOT LLVM_INCLUDE_TESTS)
     return()
@@ -38,8 +40,8 @@ function(add_libc_benchmark_unittest target_name)
   )
   target_link_libraries(${target_name}
     PRIVATE
-    llvm_gtest_main
-    llvm_gtest
+    default_gtest_main
+    default_gtest
     ${LIBC_BENCHMARKS_UNITTEST_DEPENDS}
   )
   llvm_update_compile_flags(${target_name})
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index f192cd05b5a34..c02c75f10b12f 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -1340,9 +1340,7 @@ if( LLVM_INCLUDE_UTILS )
   add_subdirectory(utils/mlgo-utils)
   add_subdirectory(utils/llvm-test-mustache-spec)
   if( LLVM_INCLUDE_TESTS )
-    set(LLVM_SUBPROJECT_TITLE "Third-Party/Google Test")
     add_subdirectory(${LLVM_THIRD_PARTY_DIR}/unittest ${CMAKE_CURRENT_BINARY_DIR}/third-party/unittest)
-    set(LLVM_SUBPROJECT_TITLE)
   endif()
 else()
   if ( LLVM_INCLUDE_TESTS )
diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 7d40d309d538e..3c3695a77cb7b 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -1802,7 +1802,13 @@ function(add_unittest test_suite test_name)
   # libpthreads overrides some standard library symbols, so main
   # executable must be linked with it in order to provide consistent
   # API for all shared libaries loaded by this executable.
-  target_link_libraries(${test_name} PRIVATE llvm_gtest_main llvm_gtest ${LLVM_PTHREAD_LIB})
+  # default_gtest should be an alias to either llvm_gtest or runtimes_gtest.
+  # If it is not defined, fall back to llvm_gtest.
+  if(TARGET default_gtest)
+    target_link_libraries(${test_name} PRIVATE default_gtest_main default_gtest ${LLVM_PTHREAD_LIB})
+  else ()
+    target_link_libraries(${test_name} PRIVATE llvm_gtest_main llvm_gtest ${LLVM_PTHREAD_LIB})
+  endif ()
 
   add_dependencies(${test_suite} ${test_name})
 endfunction()
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
index cc756da426e62..b17bd8f665361 100644
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -256,6 +256,20 @@ endif()
 # This can be used to detect whether we're in the runtimes build.
 set(LLVM_RUNTIMES_BUILD ON)
 
+# Make GTest available to all runtimes
+# The runtime must call make_gtest_target() for it to become available. This is
+# to avoid build failures when gtest is not actually needed. In particular,
+# mingw-incomplete-sysroot is missing C++ header files that GTest needs to
+# compile.
+function(build_gtest)
+  if(TARGET default_gtest)
+    # Already available
+    return()
+  endif()
+
+  add_subdirectory("${LLVM_THIRD_PARTY_DIR}/unittest" "${CMAKE_BINARY_DIR}/third-party/runtimes_gtest")
+endfunction()
+
 foreach(entry ${runtimes})
   get_filename_component(projName ${entry} NAME)
 
diff --git a/third-party/unittest/CMakeLists.txt b/third-party/unittest/CMakeLists.txt
index 3fa885a16ea1e..79535a1de4616 100644
--- a/third-party/unittest/CMakeLists.txt
+++ b/third-party/unittest/CMakeLists.txt
@@ -11,6 +11,34 @@
 #
 # Project-wide settings
 
+set(LLVM_SUBPROJECT_TITLE "Third-Party/Google Test")
+
+if(LLVM_RUNTIMES_BUILD)
+  # This instance of GTest is use for unittests for the runtime libraries. It
+  # must not link to LLVMSupport (used for llvm::raw_ostream and llvm::cl
+  # support) of the host build: It may be a different architecture and/or
+  # using a different C++ ABI such as libcxx/libstdc++.
+  set(GTEST_LLVM_COMPONENTS "")
+
+  # We cannot use llvm_gtest for the target; it would clash with
+  # find_package(LLVM) with LLVM_EXPORT_GTEST=ON. Instead, we define an alias
+  # default_gtest that points to llvm_gtest in the LLVM build and
+  # runtimes_gtest in an runtimes build.
+  set(gtest_name "runtimes_gtest")
+
+  # Override locally; never install the runtimes-GTest.
+  set(LLVM_INSTALL_GTEST OFF)
+
+  # Build the library containing main() so unittests need less boilerplate.
+  # UnitTestMain/TestMain.cpp always needs LLVMSupport, use GTest's original
+  # main when unavailable.
+  set(gtest_main_src googletest/src/gtest_main.cc)
+else()
+  set(GTEST_LLVM_COMPONENTS "Support")
+  set(gtest_name "llvm_gtest")
+  set(gtest_main_src UnitTestMain/TestMain.cpp)
+endif()
+
 if(WIN32)
   add_definitions(-DGTEST_OS_WINDOWS=1)
 endif()
@@ -38,17 +66,13 @@ if (HAVE_LIBPTHREAD)
   list(APPEND LIBS pthread)
 endif()
 
-# Make available for runtimes using the LLVM buildtree
-# (required for unittests in bootstrapping builds)
-set(EXCLUDE_FROM_ALL OFF)
-
 # Install GTest only if requested.
 set(BUILDTREE_ONLY BUILDTREE_ONLY)
 if (LLVM_INSTALL_GTEST)
   set(BUILDTREE_ONLY "")
 endif ()
 
-add_llvm_library(llvm_gtest
+add_llvm_library("${gtest_name}"
   googletest/src/gtest-all.cc
   googlemock/src/gmock-all.cc
 
@@ -56,7 +80,7 @@ add_llvm_library(llvm_gtest
   ${LIBS}
 
   LINK_COMPONENTS
-  Support # Depends on llvm::raw_ostream
+  ${GTEST_LLVM_COMPONENTS}
 
   # This is a library meant only for the build tree.
   ${BUILDTREE_ONLY}
@@ -67,15 +91,14 @@ add_llvm_library(llvm_gtest
 # that warning here for any targets that link to gtest.
 if(CXX_SUPPORTS_SUGGEST_OVERRIDE_FLAG)
   add_definitions("-Wno-suggest-override")
-  set_target_properties(llvm_gtest PROPERTIES INTERFACE_COMPILE_OPTIONS "-Wno-suggest-override")
+  set_target_properties("${gtest_name}" PROPERTIES INTERFACE_COMPILE_OPTIONS "-Wno-suggest-override")
 endif()
 
 if (NOT LLVM_ENABLE_THREADS)
-  target_compile_definitions(llvm_gtest PUBLIC GTEST_HAS_PTHREAD=0)
+  target_compile_definitions("${gtest_name}" PUBLIC GTEST_HAS_PTHREAD=0)
 endif ()
 
-# Top-level include directory required for "llvm/Support/raw_os_ostream.h"
-target_include_directories(llvm_gtest
+target_include_directories("${gtest_name}"
   PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/googletest/include>
          $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/googlemock/include>
          $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/>
@@ -84,21 +107,36 @@ target_include_directories(llvm_gtest
   PRIVATE googletest googlemock
   )
 
-# When used from the buildtree, also force use of buildtree LLVM headers,
-# (instead locally installed version)
-# FIXME: Shouldn't this be done for all LLVM libraries? Currently, LLVM uses a
-# big giant `include_directories( ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})`
-# which CMake does not add to the import library.
-target_include_directories(llvm_gtest BEFORE
-  PUBLIC $<BUILD_INTERFACE:${LLVM_SOURCE_DIR}/include>
-         $<BUILD_INTERFACE:${LLVM_BINARY_DIR}/include>
-  )
+if(LLVM_RUNTIMES_BUILD)
+  target_compile_definitions("${gtest_name}" PUBLIC GTEST_NO_LLVM_SUPPORT=1)
+else()
+  # When used from the buildtree, also force use of buildtree LLVM headers,
+  # (instead locally installed version)
+  # FIXME: Shouldn't this be done for all LLVM libraries? Currently, LLVM uses a
+  # big giant `include_directories( ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})`
+  # which CMake does not add to the import library.
+  target_include_directories("${gtest_name}" BEFORE
+    PUBLIC $<BUILD_INTERFACE:${LLVM_SOURCE_DIR}/include>
+           $<BUILD_INTERFACE:${LLVM_BINARY_DIR}/include>
+    )
+endif()
+
 
-add_subdirectory(UnitTestMain)
+add_llvm_library("${gtest_name}_main"
+  ${gtest_main_src}
+
+  LINK_LIBS
+  "${gtest_name}"
+
+  LINK_COMPONENTS
+  ${GTEST_LLVM_COMPONENTS}
+
+  ${BUILDTREE_ONLY}
+)
 
 if (LLVM_INSTALL_GTEST)
-  install(DIRECTORY googletest/include/gtest/ DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/llvm-gtest/gtest/" COMPONENT llvm_gtest)
-  install(DIRECTORY googlemock/include/gmock/ DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/llvm-gmock/gmock/" COMPONENT llvm_gtest)
+  install(DIRECTORY googletest/include/gtest/ DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/llvm-gtest/gtest/" COMPONENT "${gtest_name}")
+  install(DIRECTORY googlemock/include/gmock/ DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/llvm-gmock/gmock/" COMPONENT "${gtest_name}")
 endif()
 
 # When LLVM_LINK_LLVM_DYLIB is enabled, libLLVM.so is added to the interface
@@ -118,5 +156,14 @@ function (gtest_remove_dylib_from_link_interface target)
   endif()
 endfunction()
 
-gtest_remove_dylib_from_link_interface(llvm_gtest)
-gtest_remove_dylib_from_link_interface(llvm_gtest_main)
+if (NOT LLVM_RUNTIMES_BUILD)
+  gtest_remove_dylib_from_link_interface("${gtest_name}")
+  gtest_remove_dylib_from_link_interface("${gtest_name}_main")
+endif ()
+
+# The build processing this file always uses this GTest for unittests.
+# Projects that do not use the LLVM_ENABLE_PROJECTS mechanism, but are
+# standalone-builds using find_package(LLVM) can define these aliases
+# explicitly.
+add_library(default_gtest ALIAS "${gtest_name}")
+add_library(default_gtest_main ALIAS "${gtest_name}_main")
diff --git a/third-party/unittest/UnitTestMain/CMakeLists.txt b/third-party/unittest/UnitTestMain/CMakeLists.txt
deleted file mode 100644
index 729ea7e3fa7e2..0000000000000
--- a/third-party/unittest/UnitTestMain/CMakeLists.txt
+++ /dev/null
@@ -1,16 +0,0 @@
-set(BUILDTREE_ONLY BUILDTREE_ONLY)
-if (LLVM_INSTALL_GTEST)
-  set(BUILDTREE_ONLY "")
-endif ()
-
-add_llvm_library(llvm_gtest_main
-  TestMain.cpp
-
-  LINK_LIBS
-  llvm_gtest
-
-  LINK_COMPONENTS
-  Support # Depends on llvm::cl
-
-  ${BUILDTREE_ONLY}
-  )