cmake CMAKE_HAVE_LIBC_PTHREAD examples

apple/foundationdb cmake/FindThreads.cmake :97 

CHECK_C_SOURCE_COMPILES("${PTHREAD_C_CXX_TEST_SOURCE}" CMAKE_HAVE_LIBC_PTHREAD)

apple/foundationdb cmake/FindThreads.cmake :99 

CHECK_CXX_SOURCE_COMPILES("${PTHREAD_C_CXX_TEST_SOURCE}" CMAKE_HAVE_LIBC_PTHREAD)