[clang] [compiler-rt] [ubsan] Display correct runtime messages for negative _BitInt (PR #96240)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

The changes seem reasonable to me, but I don't have a lot of expertise with compiler-rt. Should the changes come with a release note though?

https://github.com/llvm/llvm-project/pull/96240