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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

@earnol -- given the amount of breakage, can you revert the changes to get all bots back to green, then we can re-land once you have everything fixed up?

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