build-sys: use VALGRIND not __OPTIMIZE__ as condition for valgrind compat

Actually, one might want to run valgrind even on optimized code.
Now the same check is used in the jenkins hash functions and
hashtable.

src/shared/hashmap.c

@@ -103,7 +103,7 @@ static void deallocate_tile(void **first_tile, void *p) {
         *first_tile = p;
 }
 
-#ifndef __OPTIMIZE__
+#ifdef VALGRIND
 
 static void drop_pool(struct pool *p) {
         while (p) {