Cleanup: make remaining blenlib headers work in C++

Differential Revision: https://developer.blender.org/D6988

Reviewers: brecht

source/blender/blenlib/BLI_memory_utils.h

@@ -22,9 +22,17 @@
  * \brief Generic memory manipulation API.
  */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* it may be defined already */
 #ifndef __BLI_UTILDEFINES_H__
 bool BLI_memory_is_zero(const void *arr, const size_t size);
 #endif
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* __BLI_MEMORY_UTILS_H__ */