Update valgrind.h to newer version.

src/x64/cpu-x64.cc

Index: src/x64/cpu-x64.cc
diff --git a/src/x64/cpu-x64.cc b/src/x64/cpu-x64.cc
index e637ba124de3b012d22080da417414a995d60be0..ae5045f0df8b0ca58609e9e5c444ce443e709edf 100644
--- a/src/x64/cpu-x64.cc
+++ b/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
 }