cmake LIBOMP_HAVE_ATTRIBUTE_RTM examples

Lewuathe/mlir-hello thirdparty/llvm-project/openmp/runtime/cmake/config-ix.cmake :180 

check_cxx_source_compiles("__attribute__((target(\"rtm\")))
                             int main() {return 0;}" LIBOMP_HAVE_ATTRIBUTE_RTM)