[clang] [clang-tools-extra] [NFC] Explicitly pass a VFS when creating DiagnosticsEngine (PR #115852)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-x86_64-debian` running on `lldb-x86_64-debian` while building `clang-tools-extra,clang` at step 4 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/10979

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (build) failure: build (failure)

```

</details>

https://github.com/llvm/llvm-project/pull/115852