[clang] [clang] Fix catching pointers by reference on mingw targets (PR #162546)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

@rjmccall Can you briefly look to make sure this makes sense?  (This is Itanium unwind on Windows.)

For why we're doing this, see 5add20cefac7d1b06e7892ce0d97767a23db4e1a ... but I don't really have enough context to say much beyond the explanation in the code.

https://github.com/llvm/llvm-project/pull/162546