Building librdkafka with vendored sasl for musl target fails #5242
Description
When trying to build librdkafka with vendored sasl for musl target, the build fails because cmake sets -I/usr/include for the compiler. The reason why this is happening is that we are only looking for the sasl library using pkg-config. In case we built with vendored sasl (statically linking it), the CMakeLists.txt should probably use find_package to find the library (as it does it for OpenSSL, curl, zlib, etc.). That way a vendored sasl library whose location is provided via CMAKE_PREFIX_PATH is detectable.