[x86] Use AVX in Crankshaft when available.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index c1831af84bf366c9df5a8a38d68925fad6523bf3..b3f6d03acdacc641c48eed2dacdcc61fadc09330 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -748,7 +748,8 @@ LInstruction* LChunkBuilder::DoArithmeticD(Token::Value op,
     LOperand* left = UseRegisterAtStart(instr->BetterLeftOperand());
     LOperand* right = UseRegisterAtStart(instr->BetterRightOperand());
     LArithmeticD* result = new(zone()) LArithmeticD(op, left, right);
-    return DefineSameAsFirst(result);
+    return CpuFeatures::IsSupported(AVX) ? DefineAsRegister(result)
+                                         : DefineSameAsFirst(result);
   }
 }