FindThreads: Honor THREADS_PREFER_PTHREAD_FLAG when pthread is found in libc
The -pthread
flag tells the compiler/linker to link to additional
libraries needed for thread support (e.g. libatomic on riscv64). The
flag therefore should be used if requested using
THREADS_PREFER_PTHREAD_FLAG
also when the pthread functions are
found in libc.
This backports !6693 (merged) to to CMake 3.21 and 3.22 branches.
Backport: release
Edited by Brad King