[clang] [Clang] Implement P2864R2 Remove Deprecated Arithmetic Conversion on… (PR #73105)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM -- I'm a bit worried about breaking working code, but the user has to explicitly opt into C++26 mode and so it's only slightly unreasonable for them to have to change their previously correct, working code because of this. I say we leave it as an error, but if users complain about this being too strict, we can relax it to be a warning that defaults to an error or just leave it deprecated and support it forever.

https://github.com/llvm/llvm-project/pull/73105