[flang] [llvm] [Flang][OpenMP] Add semantic checks for order clause (PR #115281)

[Thirumalai Shaktivel via llvm-commits]

Thirumalai-Shaktivel wrote:

Okay, I got it.

Shall we keep the following restrictions, then:
```
OpenMP 5.2: 10.3 Order clause restrictions

- If a threadprivate variable is referenced inside a region that corresponds to a construct with an order clause that specifies concurrent, the behavior is unspecified.

OpenMP 5.1:
2.11.3 order Clause restriction:

- At most one order clause may appear on a construct.
```

https://github.com/llvm/llvm-project/pull/115281