Update valgrind.h. Codereview http://codereview.chromium.org/7468002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8721 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/cpu-x64.cc

@@ -67,7 +67,8 @@ void CPU::FlushICache(void* start, size_t size) {
   // solution is to run valgrind with --smc-check=all, but this comes at a big
   // performance cost.  We can notify valgrind to invalidate its cache.
 #ifdef VALGRIND_DISCARD_TRANSLATIONS
-  VALGRIND_DISCARD_TRANSLATIONS(start, size);
+  unsigned res = VALGRIND_DISCARD_TRANSLATIONS(start, size);
+  USE(res);
 #endif
 }