[clang] [llvm] [ARM] Add support for Windows SEH (PR #184953)

[Hans Wennborg via cfe-commits]

https://github.com/zmodem commented:

Learning about SEH is on my todo list, but I never seem to get to it. I see Reid, Martin and Eli are on the review already and they actually know stuff.

(If folks on this PR have reading suggestions, please share. :)

https://github.com/llvm/llvm-project/pull/184953