[clang] [clang-tools-extra] [clang] Extend diagnose_if to accept more detailed warning information (PR #70976)

[Mikael Holmén via cfe-commits]

mikaelholmen wrote:

Hello,

I noticed that before this patch
```clang empty.c -fsanitize=undefined -ffine-grained-bitfield-accesses -c -Werror```
(on empty file empty.c) resulted in
```warning: option '-ffine-grained-bitfield-accesses' cannot be enabled together with a sanitizer; flag ignored```
but with the patch it results in
```error: option '-ffine-grained-bitfield-accesses' cannot be enabled together with a sanitizer; flag ignored [-Werror]```

Is this on purpose?

(I originally asked this in
 https://github.com/llvm/llvm-project/pull/108453#issuecomment-2352155766
but I suppose this PR has a bit wider audience.)

https://github.com/llvm/llvm-project/pull/70976