[Flang][OpenMP] Allow copyprivate and nowait on the directive clauses (#127769)

Issue:
- Single construct used to throw a semantic error for copyprivate and
  nowait clause when used in the single directive.
- Also, the copyprivate with nowait restriction has been removed from
  OpenMP 6.0

Fix:
- Allow copyprivate and nowait on both single and end single directive
- Allow at most one nowait clause
- Throw a warning when the same list item is used in the copyprivate clause
  on the end single directive

From Reference guide (OpenMP 5.2, 2.10.2):
```
!$omp single [clause[ [,]clause] ... ]
loosely-structured-block
!$omp end single [end-clause[ [,]end-clause] ...]

clause:
  copyprivate (list)
  nowait
  [...]

end-clause:
  copyprivate (list)
  nowait
```

Towards: https://github.com/llvm/llvm-project/issues/110008

0 files changed, 0 insertions, 0 deletions