[llvm] [cmake] Hardcode some `check_include_file` checks (PR #104706)

[Aaron Ballman via llvm-commits]

https://github.com/AaronBallman approved this pull request.

LGTM with a minor cleanup. Any final concerns @petrhosek or @Ericson2314?

https://github.com/llvm/llvm-project/pull/104706