[clang] [llvm] [clang] Simplify usage of FileManager::makeAbsolutePath (PR #182360)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `clang,llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/39302

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

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR :: mlir-tblgen/op-attribute.td (3871 of 3882)
PASS: MLIR :: mlir-tblgen/op-interface.td (3872 of 3882)
PASS: MLIR :: mlir-translate/split-markers.mlir (3873 of 3882)
PASS: MLIR :: Pass/pipeline-parsing.mlir (3874 of 3882)
PASS: MLIR :: Pass/ir-printing.mlir (3875 of 3882)
PASS: MLIR :: Pass/pass-timing.mlir (3876 of 3882)
PASS: MLIR :: mlir-tblgen/llvm-intrinsics.td (3877 of 3882)
PASS: MLIR :: mlir-tblgen/op-error.td (3878 of 3882)
PASS: MLIR :: mlir-runner/utils.mlir (3879 of 3882)
PASS: MLIR :: Pass/pipeline-options-parsing.mlir (3880 of 3882)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1852.857272

```

</details>

https://github.com/llvm/llvm-project/pull/182360