Make Win32 put the SRet address into EAX, fixes PR15556

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178291 91177308-0d34-0410-b5e6-96231b3b80d8
These two are default in the constructor for MCAsmInfo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178293 91177308-0d34-0410-b5e6-96231b3b80d8