c11: Fixes unused parameter warnings

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15553>

include/c11/threads_win32.h

@@ -228,6 +228,7 @@ cnd_broadcast(cnd_t *cond)
 static inline void
 cnd_destroy(cnd_t *cond)
 {
+    (void)cond;
     assert(cond != NULL);
     // do nothing
 }
@@ -456,6 +457,7 @@ thrd_join(thrd_t thr, int *res)
 static inline void
 thrd_sleep(const struct timespec *time_point, struct timespec *remaining)
 {
+    (void)remaining;
     assert(time_point);
     assert(!remaining); /* not implemented */
     Sleep((DWORD)impl_timespec2msec(time_point));