[EH] Create removeUnwindEdge utility

[EH] Create removeUnwindEdge utility

Summary:
Factor the code that rewrites invokes to calls and rewrites WinEH
terminators to their "unwind to caller" equivalents into a helper in
Utils/Local, and use it in the three places I'm aware of that need to do
this.

Reviewers: andrew.w.kaylor, majnemer, rnk

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13152

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248677 91177308-0d34-0410-b5e6-96231b3b80d8