do not declare malloc etc. if not needed

include/dmmlib/dmmlib.h

@@ -34,6 +34,8 @@
 /** Global variable storing allocator's settings */
 allocator_t systemallocator;
 
+#if !defined _STDLIB_H && !defined _STDLIB_H_
+
 /**
  * Allocates size bytes by using the system's allocator.
  * @param size Requested allocation size in bytes.
@@ -66,4 +68,6 @@ void * realloc(void *ptr, size_t size);
  */
 void * calloc(size_t count, size_t size);
 
+#endif /* ! STDLIB_H */
+
 #endif /* DMMLIB_H */