[WinEH] Permit branch folding in the face of funclets

Track which basic blocks belong to which funclets.  Permit branch
folding to fire but only if it can prove that doing so will not cause
code in one funclet to be reused in another.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249257 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed