Clang/mac: Get unit_tests built.

testing/gmock/include/gmock/gmock-actions.h

 // Copyright 2007, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 516 matching lines @@
     return NULL;
   }
 };
 
 // Implements the Return() action.
 class ReturnVoidAction {
  public:
   // Allows Return() to be used in any void-returning function.
   template <typename Result, typename ArgumentTuple>
   static void Perform(const ArgumentTuple&) {
-    CompileAssertTypesEqual<void, Result>();
+    (void)CompileAssertTypesEqual<void, Result>();
   }
 };
 
 // Implements the polymorphic ReturnRef(x) action, which can be used
 // in any function that returns a reference to the type of x,
 // regardless of the argument types.
 template <typename T>
 class ReturnRefAction {
  public:
   // Constructs a ReturnRefAction object from the reference to be returned.
@@ skipping 471 matching lines @@
 //
 //   ByRef<const Base>(derived)
 template <typename T>
 inline internal::ReferenceWrapper<T> ByRef(T& l_value) {  // NOLINT
   return internal::ReferenceWrapper<T>(l_value);
 }
 
 }  // namespace testing
 
 #endif  // GMOCK_INCLUDE_GMOCK_GMOCK_ACTIONS_H_