[WinEH] Fix cleanup state numbering

Summary:
 - Recurse from cleanupendpads to their cleanuppads, to make sure the
   cleanuppad is visited if it has a cleanupendpad but no cleanupret.
 - Check for and avoid double-processing cleanuppads, to allow for them to
   have multiple cleanuprets (plus cleanupendpads).
 - Update Cxx state numbering to visit toplevel cleanupendpads and to
   recurse from cleanupendpads to their preds, to ensure we number any
   funclets in inlined cleanups.  SEH state numbering already did this.

Reviewers: rnk

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13374

llvm-svn: 249792