[WinEH] Stop BranchFolding from merging across funclets

BranchFolding would merge two funclets together, this is not OK.
Disable this and strengthen the assertion in FuncletLayout.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249069 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed