cmake LIBOMP_HAVE_ATTRIBUTE_WAITPKG examples

Lewuathe/mlir-hello thirdparty/llvm-project/openmp/runtime/cmake/config-ix.cmake :182 

check_cxx_source_compiles("__attribute__((target(\"waitpkg\")))
                            int main() {return 0;}" LIBOMP_HAVE_ATTRIBUTE_WAITPKG)