va_args support for Win64.
Patch by Cameron!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115480 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp
index 4e435ee..ad2980e 100644
--- a/lib/Target/X86/X86TargetMachine.cpp
+++ b/lib/Target/X86/X86TargetMachine.cpp
@@ -121,8 +121,7 @@
     Subtarget(TT, FS, is64Bit),
     FrameInfo(TargetFrameInfo::StackGrowsDown,
               Subtarget.getStackAlignment(),
-              (Subtarget.isTargetWin64() ? -40 :
-               (Subtarget.is64Bit() ? -8 : -4))),
+              Subtarget.is64Bit() ? -8 : -4),
     ELFWriterInfo(is64Bit, true) {
   DefRelocModel = getRelocationModel();