[clang] [CLANG] Enable alignas after GNU attributes (PR #133107)

[via cfe-commits]

https://github.com/Sirraide commented:

At a glance this *does* seem like the right place to do this, but this is still missing a release note.

It seems like GCC allows e.g. `__attribute__(()) alignas(16) int x` in any case, so I don’t see why we shouldn’t allow this too. Can you also add some tests that use `__attribute__(())` directly and which aren’t CUDA-specific? 

Oh, and can you add solmething like this as a test as well:
```c++
struct S { __attribute__((deprecated)) alignas(16) int x; };
```

https://github.com/llvm/llvm-project/pull/133107