Fix the dtor location issues in PR20038 harder.

Originally committed in r211722, this fixed one case of dtor calls being
emitted without locations (this causes problems for debug info if the
call is then inlined), this caught only some of the cases.

Instead of trying to re-enable the location before the cleanup, simply
re-enable the location immediately after the unconditional branches in
question using a scoped device to ensure the no-location state doesn't
leak out arbitrarily.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212761 91177308-0d34-0410-b5e6-96231b3b80d8