[clang] [clang][deps] Prefer `DiagnosticConsumer` over `llvm::{Error,Expected}` (PR #172389)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 82063 tests passed
* 1171 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang-Unit
<details>
<summary>Clang-Unit._/AllClangUnitTests/DependencyScanner/ScanDepsWithModuleLookup</summary>

```
Script:
--
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/unittests/./AllClangUnitTests --gtest_filter=DependencyScanner.ScanDepsWithModuleLookup
--
/home/gha/actions-runner/_work/llvm-project/llvm-project/clang/unittests/Tooling/DependencyScannerTest.cpp:301
Value of: DepFile.has_value()
  Actual: true
Expected: false


```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/172389