[flang] [llvm] [flang][OpenMP] Change clause modifier representation in parser (PR #116656)

[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-g3-04` while building `flang,llvm` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/4019

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[7867/8757] Building CXX object tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/check-arithmeticif.cpp.o
[7868/8757] Building CXX object tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/check-call.cpp.o
[7869/8757] Building CXX object tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/check-case.cpp.o
[7870/8757] Building CXX object tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/check-coarray.cpp.o
[7871/8757] Building CXX object tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/check-cuda.cpp.o
[7872/8757] Linking CXX static library lib/libFortranParser.a
[7873/8757] Linking CXX executable bin/clang-tidy
[7874/8757] Building CXX object tools/clang/tools/extra/clangd/CMakeFiles/obj.clangDaemon.dir/Diagnostics.cpp.o
[7875/8757] Building CXX object tools/clang/tools/extra/clangd/CMakeFiles/obj.clangDaemon.dir/XRefs.cpp.o
[7876/8757] Building CXX object tools/clang/tools/libclang/CMakeFiles/libclang.dir/CXExtractAPI.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=1773.908121

```

</details>

https://github.com/llvm/llvm-project/pull/116656