[util/malloc-stats.c] Add a public function malloc_stats()

Apparently glibc already provides the function:

  void malloc_stats (void);

So, like we do for backtrace_symbols(), override the public symbol.
It still is defined as __destructor__ and runs at program finalization.

util/malloc-stats.c

@@ -275,8 +275,8 @@ merge_similar_entries (void)
 }
 
 __attribute__ ((destructor))
-static void
-finish (void)
+void
+malloc_stats (void)
 {
 	int i;
 
@@ -298,4 +298,3 @@ finish (void)
 		}
 	}
 }
-