[clang] [Clang] Treat line directives as header names. (PR #211512)

[via cfe-commits]

github-actions[bot] wrote:

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

* 90499 tests passed
* 1710 tests skipped
* 1 test failed

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

### Clangd Unit Tests
<details>
<summary>Clangd Unit Tests._/ClangdTests/PreamblePatchTest/MainFileIsEscaped</summary>

```
Script:
--
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/clangd/unittests/./ClangdTests --gtest_filter=PreamblePatchTest.MainFileIsEscaped
--
/home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/clangd/unittests/PreambleTests.cpp:178
Value of: Includes
Expected: has 1 element that (is an object whose given field is equal to "<a.h>") and (is an object whose given field is equal to 0)
  Actual: {}


```
</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/211512