[clang] [AST] Make err_struct_too_large check target-aware (PR #218749)

[Akira Hatanaka via cfe-commits]

ahatanak wrote:

> This change needs a release note. Please add an entry to `clang/docs/ReleaseNotes.md` in the section the most adapted to the change, and referencing any Github issue this change fixes. Thanks!

I searched but couldn't find any existing Github issue for this.

https://github.com/llvm/llvm-project/pull/218749