Revert "Proper va_arg/va_copy lowering on win64"

This reverts commit 2b52880592a525cfe04d8f9008a35da8c2ea94c3.

Needs review.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185806 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index a6e894b..174cc46 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -582,12 +582,10 @@
   // VASTART needs to be custom lowered to use the VarArgsFrameIndex
   setOperationAction(ISD::VASTART           , MVT::Other, Custom);
   setOperationAction(ISD::VAEND             , MVT::Other, Expand);
-  if (Subtarget->is64Bit() && !Subtarget->isTargetWin64()) {
-    // TargetInfo::X86_64ABIBuiltinVaList
+  if (Subtarget->is64Bit()) {
     setOperationAction(ISD::VAARG           , MVT::Other, Custom);
     setOperationAction(ISD::VACOPY          , MVT::Other, Custom);
   } else {
-    // TargetInfo::CharPtrBuiltinVaList
     setOperationAction(ISD::VAARG           , MVT::Other, Expand);
     setOperationAction(ISD::VACOPY          , MVT::Other, Expand);
   }