[clang] [compiler-rt] [ubsan] Display correct runtime messages for negative _BitInt (PR #93612)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

In addition to the issue noted on buildbots, this also caused failed tests on i386:
https://github.com/mstorsjo/llvm-mingw/actions/runs/9606458336/job/26504129718#step:8:1501

There seem to be a couple of different errors there:
```
bit-int.c:72:19: runtime error: implicit conversion from type 'unsigned _BitInt(37)' of value [21707795506135039](tel:21707795506135039) (64-bit, unsigned) to type '_BitInt(37)' changed the value to -1 (64-bit, signed)

AddressSanitizer: CHECK failed: ubsan_value.cpp:87 "((0 && "libclang_rt.ubsan was built without __int128 support")) != (0)" (0x0, 0x0) (tid=2296)

```

https://github.com/llvm/llvm-project/pull/93612