[clang] [clang] Don't crash in invalid #module directive (PR #208695)

[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` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/48200

<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/OpenACC/acc-implicit-data-fortran.F90 (4686 of 4696)
PASS: Flang :: Driver/nostdlib.f90 (4687 of 4696)
PASS: Flang :: Driver/linker-flags.f90 (4688 of 4696)
PASS: Flang :: Driver/fveclib.f90 (4689 of 4696)
PASS: Flang :: Driver/options-loongarch.f90 (4690 of 4696)
PASS: Flang :: Driver/mrecip.f90 (4691 of 4696)
PASS: Flang :: Driver/linker-options.f90 (4692 of 4696)
PASS: Flang :: Driver/fopenmp.f90 (4693 of 4696)
PASS: Flang :: Driver/mcmodel.f90 (4694 of 4696)
PASS: Flang :: Driver/omp-driver-offload.f90 (4695 of 4696)
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=4128.992569

```

</details>

https://github.com/llvm/llvm-project/pull/208695