[clang] [clang-tools-extra] Revert "[clang] Don't add documentation comments to the AST if not requested" (PR #219807)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `clang-tools-extra,clang` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/50566

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

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
PASS: Flang :: Transforms/debug-line-table-inc-same-file.fir (4955 of 4966)
PASS: Flang :: Transforms/debug-line-table.fir (4956 of 4966)
PASS: Flang :: Lower/math-lowering/sinh.f90 (4957 of 4966)
PASS: Flang :: Lower/math-lowering/tan.f90 (4958 of 4966)
PASS: Flang :: Driver/omp-driver-offload.f90 (4959 of 4966)
PASS: Flang :: Driver/openacc-nyi.f90 (4960 of 4966)
PASS: Flang :: Lower/OpenMP/requires-notarget.f90 (4961 of 4966)
PASS: Flang :: Lower/OpenMP/requires-usm.f90 (4962 of 4966)
PASS: Flang :: Transforms/verify-known-runtime-functions.fir (4963 of 4966)
PASS: Flang :: Transforms/vscale-attr.fir (4964 of 4966)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=3163.601386

```

</details>

https://github.com/llvm/llvm-project/pull/219807