cmake HAVE_POPCNT examples

pingcap/tiflash cmake/cpu_features.cmake :167 

check_cxx_source_compiles("
        int main() {
            auto a = __builtin_popcountll(0);
            (void)a;
            return 0;
        }
    " HAVE_POPCNT)

ByConity/ByConity cmake/cpu_features.cmake :98 

check_cxx_source_compiles("
        int main() {
            auto a = __builtin_popcountll(0);
            (void)a;
            return 0;
        }
    " HAVE_POPCNT)