[llvm] [Windows SEH] fix failed assert and crash (PR #107031)

[via llvm-commits]

R-Goc wrote:

I'm having trouble getting the reproducer to be an .ll or .bc file. It seems even less deterministic in that form. For example debug llc doesn't hang on it.  Bugpoint fails to emit a proper file as well. Currently there are 3 known reproductions, 2 of which are very delicate and fail with seemingly unrelated options. The one that basically always fails is a 350k loc part of protobufs. 

https://github.com/llvm/llvm-project/pull/107031