Don't crash on leaving nested __finally blocks through an EH edge.

Don't crash on leaving nested __finally blocks through an EH edge.

The __finally emission block tries to be clever by removing unused continuation
edges if there's an unconditional jump out of the __finally block. With
exception edges, the EH continuation edge isn't always unused though and we'd
crash in a few places.

Just don't be clever. That makes the IR for __finally blocks a bit longer in
some cases (hence small and behavior-preserving changes to existing tests), but
it makes no difference in general and it fixes the last crash from PR22553.

http://reviews.llvm.org/D7918

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@230697 91177308-0d34-0410-b5e6-96231b3b80d8