cmake SAIL_HAVE_BUILTIN_BSWAP16 examples

HappySeaFox/sail CMakeLists.txt :343 

message("* SAIL_HAVE_BUILTIN_BSWAP16:    ${SAIL_HAVE_BUILTIN_BSWAP16_DISPLAY}")

HappySeaFox/sail cmake/sail_check_builtin_bswap.cmake :5 

check_c_source_compiles(
        "
            int main(int argc, char *argv[]) {
                __builtin_bswap16(0);
                return 0;
            }
        "
        SAIL_HAVE_BUILTIN_BSWAP16
        )