cmake SAIL_HAVE_THREAD_LOCAL examples

HappySeaFox/sail cmake/sail_check_c11_thread_local.cmake :7

check_c_source_compiles(
            "
            #include \"sail-common/compiler_specifics.h\"

            int main(int argc, char *argv[]) {
                static SAIL_THREAD_LOCAL int i = 0;
                return 0;
            }
        "
        SAIL_HAVE_THREAD_LOCAL
        )