[clang] [Clang] Improve EmitClangAttrSpellingListIndex (PR #114899)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This seems to have missed a bunch, see `alloc_size` and `allocating` and `alloc_align`, all of which are the same spellings, but you're checking the name anyway (in the .inc file you linked).

There are actually quite a lot of cases you're not covering there, and the loop you did to generate this is a bit out of hand.  I've suggested some simplifications.

https://github.com/llvm/llvm-project/pull/114899