[clang] [Clang][CodeGen][UBSan] Add more precise attributes to recoverable ubsan handlers (PR #130990)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

> The ubsan handler cannot be eliminated because inaccessiblemem: readwrite indicates that it has externally observable side effects.

That is not how things work.  For example:

```
$ echo "declare void @g() define void @f() nounwind { call void @g() memory(argmem: read, inaccessiblemem: readwrite) willreturn unreachable }" | opt -O3 -S
; ModuleID = '<stdin>'
source_filename = "<stdin>"

; Function Attrs: mustprogress nofree norecurse noreturn nosync nounwind willreturn memory(none)
define void @f() local_unnamed_addr #0 {
  unreachable
}

attributes #0 = { mustprogress nofree norecurse noreturn nosync nounwind willreturn memory(none) }
```


https://github.com/llvm/llvm-project/pull/130990