[clang] [Clang] Added check for unexpanded pack in attribute [[assume]] (PR #91893)

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Sirraide wrote:

> I have received two emails from llvm build bot regarding failed builds, though the commit shows 8 build fails.

That need not be because of this pr specifically; it may just be that someone else did something that caused the build to fail, and the commit for this pr just happened to be among the commits that was tested. Can you put the buildbot link here so we can take a look at it?

https://github.com/llvm/llvm-project/pull/91893