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

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

I ran the C++ through creduce to cut it down to something llvm-reduce wouldn't crash on (it seemed to quickly bail on an invoke IIRC, perhaps not adapted to Windows-style exceptions), and then ran it through llvm-reduce to get a minimal IR test.

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