SDL_malloc.c: fix variable 'used' set but not used Emitted by clang-cl
diff --git a/src/stdlib/SDL_malloc.c b/src/stdlib/SDL_malloc.c
index 1e986f6..093a2a0 100644
--- a/src/stdlib/SDL_malloc.c
+++ b/src/stdlib/SDL_malloc.c
@@ -3017,6 +3017,8 @@ internal_malloc_stats(mstate m)
(unsigned long) (maxfp));
fprintf(stderr, "system bytes = %10lu\n", (unsigned long) (fp));
fprintf(stderr, "in use bytes = %10lu\n", (unsigned long) (used));
+#else
+ (void)used;
#endif
POSTACTION(m);