hide dependency-triggering pointer object in malloc_usable_size.c

src/malloc/malloc_usable_size.c

 #include <malloc.h>
 #include "malloc_impl.h"
-
-void *(*const __realloc_dep)(void *, size_t) = realloc;
+ 
+hidden void *(*const __realloc_dep)(void *, size_t) = realloc;
 
 size_t malloc_usable_size(void *p)
 {