[Flang][OpenMP] Fix to construct-names inside OpenMP construct with default(none) (#82479)

When a do loop with a construct-name is used inside OpenMP construct
with default(none), an incorrect error will be raised as below.

```
program cn_and_default
    implicit none
    integer :: i

    !$omp parallel default(none)
        loop: do i = 1, 10
        end do loop
    !$omp end parallel
end program
```

> The DEFAULT(NONE) clause requires that 'loop' must be listed in a
data-sharing attribute clause

This patch fixes this by adding a condition to check and skip processing
construct-names.