c11: Fixes memory leak of pack in thrd_create on win32

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15087>

src/c11/impl/threads_win32.c

@@ -319,6 +319,7 @@ thrd_create(thrd_t *thr, thrd_start_t func, void *arg)
     pack->arg = arg;
     handle = _beginthreadex(NULL, 0, impl_thrd_routine, pack, 0, NULL);
     if (handle == 0) {
+        free(pack);
         if (errno == EAGAIN || errno == EACCES)
             return thrd_nomem;
         return thrd_error;