[flang] [llvm] [flang][OpenMP] Parse WHEN, OTHERWISE, MATCH clauses plus METADIRECTIVE (PR #121817)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla` running on `linaro-g3-01` while building `flang,llvm` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/5442

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[1434/1677] Linking CXX shared library lib/libclang.so.21.0.0git
[1435/1677] Creating library symlink lib/libclang.so.21.0git lib/libclang.so
[1436/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/Mangler.cpp.o
[1437/1677] Linking CXX executable bin/c-arcmt-test
[1438/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/ConvertVariable.cpp.o
[1439/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/ConvertType.cpp.o
[1440/1677] Linking CXX executable bin/c-index-test
[1441/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/HostAssociations.cpp.o
[1442/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/IO.cpp.o
[1443/1677] Building CXX object tools/flang/lib/Lower/CMakeFiles/FortranLower.dir/IterationSpace.cpp.o
command timed out: 1200 seconds without output running [b'ninja'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2476.086944

```

</details>

https://github.com/llvm/llvm-project/pull/121817