cmake PLIBSYS_HAS_XLC_VISIBILITY examples

saprykin/plibsys cmake/VisibilityDetect.cmake :73

check_c_source_compiles ("int main () {
                                        #if (defined(__xlC__) && (__xlC__ >= 0x0D01))
                                        return 0;
                                        #else
                                        stop_compile_here
                                        #endif
                                 }"
                                 PLIBSYS_HAS_XLC_VISIBILITY
        )