[WinEH] Don't visit the same catchswitch twice

[WinEH] Don't visit the same catchswitch twice

We visited the same catchswitch twice because it was both the child of
another funclet and the predecessor of a cleanuppad.

Instead, change the numbering algorithm to only recurse if the unwind
destination of the inner funclet agrees with the unwind destination of
the catchswitch.

This fixes PR25926.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256317 91177308-0d34-0410-b5e6-96231b3b80d8