cmake PLIBSYS_HAS_CLANG_VISIBILITY examples

saprykin/plibsys cmake/VisibilityDetect.cmake :108

check_c_source_compiles ("int main () {
                                        #if defined(__has_attribute) && __has_attribute(visibility)
                                        return 0;
                                        #else
                                        stop_compile_here
                                        #endif
                                 }"
                                 PLIBSYS_HAS_CLANG_VISIBILITY
        )