[WinEH] Update to new EH pad/ret signatures (with tokens required)

Summary:
The signatures of the methods in LLVM for creating EH pads/rets are changing
to require token arguments on rets and assume token return type on pads.
Update creation code accordingly.

Reviewers: majnemer, rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D12109

llvm-svn: 245798