[X86] Support avx/avx2 by default.

Author: gmh5225

llvm/lib/TargetParser/X86TargetParser.cpp

@@ -633,6 +633,8 @@ void llvm::X86::getFeaturesForCPU(StringRef CPU,
   Bits |= FeatureSSE3;
   Bits |= FeatureSSE4_1;
   Bits |= FeatureSSE4_2;
+  Bits |= FeatureAVX;
+  Bits |= FeatureAVX2;
   Bits |= FeatureINVPCID;
   Bits |= FeatureRTM;
 #endif