[clang] [llvm] [OpenMP 60] Update parsing and semantic support for `nowait` clause to accept optional argument (PR #159628)

[Fazlay Rabbi via llvm-commits]

mdfazlay wrote:

> IIRC, you'll need to handle capturing just like for if clause

`ParseOpenMPSingleExprWithArgClause` function is used to parse `if` clause as it accepts an optional directive modifier. But that is not the case for `nowait` clause as it only accepts an optional expr (no modifier), hence I used `ParseOpenMPSingleExprClause`. Please take a look and let me know if I missed s/t. Thank you, Alexey!

https://github.com/llvm/llvm-project/pull/159628