GOMP: OMP 5.1: simd construct for non-pointer random access iterators

[Grosse-Bley, Paul Leonard]

Hi together,

I just ran into the issue that `#pragma omp simd` does not work on C++ iterator loops (godbolt).
>From going through the specifications I understand that this restriction was part of 4.5 and 5.0, but was dropped with 5.1.
As I couldn't find this change in the table of 5.1 (or 5.2) features for libgomp, I wanted to ask if this is on the horizon.

Best,
Paul Große-Bley