[llvm] [Frontend][OpenMP] Add `order` clause as allowed for `distribute` (PR #90689)

[Kiran Chandramohan via llvm-commits]

https://github.com/kiranchandramohan approved this pull request.

For Flang this is only currently used for checking which clauses are allowed in which constructs. At the moment this will lead to an error. With this change it will pass. Adding a test might be good.

```
$ ./bin/flang-new -fopenmp nb.f90
error: Semantic errors in nb.f90
./nb.f90:10:20: error: ORDER clause is not allowed on the DISTRIBUTE directive
    !$omp distribute order(concurrent)
```

Please wait for @alexey-bataev for the Clang side.

https://github.com/llvm/llvm-project/pull/90689