cmake SAIL_HAVE_BUILTIN_BSWAP64 examples

HappySeaFox/sail CMakeLists.txt :345 

message("* SAIL_HAVE_BUILTIN_BSWAP64:    ${SAIL_HAVE_BUILTIN_BSWAP64_DISPLAY}")

HappySeaFox/sail cmake/sail_check_builtin_bswap.cmake :41 

check_c_source_compiles(
        "
            int main(int argc, char *argv[]) {
                __builtin_bswap64(0);
                return 0;
            }
        "
        SAIL_HAVE_BUILTIN_BSWAP64
        )