Be sure to destroy the normal entry block of a cleanup that we

aren't actually going to make a normal cleanup for.  Sometimes
we optimistically create branches to such blocks for fixups,
and then we resolve the fixup to somewhere within the cleanup's
scope, and then the cleanup is actually not reachable for some
reason.  The process of resolving the fixup leaves us with
switches whose default edge leads to the cleanup;  we can
replace that with unreachable, then (in many cases) turn
the switch into an unconditional branch.

Fixes PR10467.

llvm-svn: 137011