Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp	(revision 79237)
+++ lib/Basic/Targets.cpp	(working copy)
@@ -918,6 +918,7 @@
     DefineStd(Defines, "WINNT", Opts);
     Define(Defines, "_X86_");
     Define(Defines, "__MSVCRT__");
+    Define(Defines, "_M_IX86");
   }
 
   virtual void getDefaultLangOptions(LangOptions &Opts) {