clang/win: Let SK_TRACEHR not produce -Wunused-value warnings in release builds.

include/utils/win/SkHRESULT.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkHRESULT_DEFINED
 #define SkHRESULT_DEFINED
 
 #include "SkTypes.h"
 #ifdef SK_BUILD_FOR_WIN
 
 void SkTraceHR(const char* file, unsigned long line,
                HRESULT hr, const char* msg);
 
 #ifdef SK_DEBUG
 #define SK_TRACEHR(_hr, _msg) SkTraceHR(__FILE__, __LINE__, _hr, _msg)
 #else
-#define SK_TRACEHR(_hr, _msg) _hr
+#define SK_TRACEHR(_hr, _msg) sk_ignore_unused_variable(_hr)
 #endif
 
 #define HR_GENERAL(_ex, _msg, _ret) {\
     HRESULT _hr = _ex;\
     if (FAILED(_hr)) {\
         SK_TRACEHR(_hr, _msg);\
         return _ret;\
     }\
 }
 
@@ skipping 20 matching lines @@
 #define HRNM(ex, msg) HR_GENERAL(ex, msg, NULL)
 
 #define HRV(ex) HR_GENERAL(ex, NULL, )
 #define HRVM(ex, msg) HR_GENERAL(ex, msg, )
 
 #define HRZ(ex) HR_GENERAL(ex, NULL, 0)
 #define HRZM(ex, msg) HR_GENERAL(ex, msg, 0)
 //@}
 #endif  // SK_BUILD_FOR_WIN
 #endif  // SkHRESULT_DEFINED