[clang] [BoundsSafety] Allow 'counted_by' attribute on pointers in structs in C (PR #90786)

[Dan Liew via cfe-commits]

delcypher wrote:

@kees @bwendling @rapidsna The workaround to downgrade this error to a warning has landed
https://github.com/llvm/llvm-project/commit/cef6387e52578366c2332275dad88b9953b55336

https://github.com/llvm/llvm-project/pull/90786