dutil: Adopt the zalloc()/zfree() from perf

So that we handle const pointers, also zalloc() is much simpler just
calling calloc(1, size).

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

dutil.c

@@ -13,12 +13,15 @@
 #include <stdlib.h>
 #include <string.h>
 
-void *zalloc(const size_t size)
+void *zalloc(size_t size)
 {
-	void *s = malloc(size);
-	if (s != NULL)
-		memset(s, 0, size);
-	return s;
+        return calloc(1, size);
+}
+
+void __zfree(void **ptr)
+{
+        free(*ptr);
+        *ptr = NULL;
 }
 
 struct str_node *str_node__new(const char *s, bool dupstr)
@@ -44,7 +47,7 @@ out_delete:
 static void str_node__delete(struct str_node *snode, bool dupstr)
 {
 	if (dupstr)
-		free((void *)snode->s);
+		zfree(&snode->s);
 	free(snode);
 }
 

dutil.h

@@ -336,6 +336,8 @@ static inline int elf_getshdrstrndx(Elf *elf, size_t *dst)
 
 char *strlwr(char *s);
 
-#define zfree(ptr) ({ free(*ptr); *ptr = NULL; })
+void __zfree(void **ptr);
+
+#define zfree(ptr) __zfree((void **)(ptr))
 
 #endif /* _DUTIL_H_ */