Proper va_arg/va_copy lowering on win64

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185763 91177308-0d34-0410-b5e6-96231b3b80d8
[objc-arc] When we initialize ARCRuntimeEntryPoints, make sure we reset all references to entrypoint declarations as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185764 91177308-0d34-0410-b5e6-96231b3b80d8