Fix compilation with clang 5.1 on OS X.

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems 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.
 //
@@ skipping 202 matching lines @@
 // -----------------------------------------------------------------------------
 // Implementation of PlatformFeatureScope
 
 PlatformFeatureScope::PlatformFeatureScope(Isolate* isolate, CpuFeature f)
     : isolate_(isolate), old_cross_compile_(CpuFeatures::cross_compile_) {
   // CpuFeatures is a global singleton, therefore this is only safe in
   // single threaded code.
   ASSERT(Serializer::enabled());
   uint64_t mask = static_cast<uint64_t>(1) << f;
   CpuFeatures::cross_compile_ |= mask;
+  USE(isolate_);
 }
 
 
 PlatformFeatureScope::~PlatformFeatureScope() {
   CpuFeatures::cross_compile_ = old_cross_compile_;
 }
 
 
 // -----------------------------------------------------------------------------
 // Implementation of Label
@@ skipping 1394 matching lines @@
       r2 = r2 - ad;
     }
     delta = ad - r2;
   } while (q1 < delta || (q1 == delta && r1 == 0));
   int32_t mul = static_cast<int32_t>(q2 + 1);
   multiplier_ = (d < 0) ? -mul : mul;
   shift_ = p - 32;
 }
 
 } }  // namespace v8::internal