[clang] [CIR] Refactor include guards to use a consistent naming (NFC) (PR #148849)

[Henrich Lauko via cfe-commits]

xlauko wrote:

### Merge activity

* **Jul 15, 2:11 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/148849).


https://github.com/llvm/llvm-project/pull/148849