[OpenMP] Fix `present` diagnostic for array extension

For example, without this patch, the following fails as expected with
or without the `present` modifier, but the `present` modifier doesn't
produce its usual diagnostic:

```
 #pragma omp target data map(alloc: arr[0:2])
 {
   #pragma omp target map(present, tofrom: arr[0:100]) // not fully present
   ;
 }
```

Reviewed By: grokos, vzakhari

Differential Revision: https://reviews.llvm.org/D85320