Invalid namelist concatenation in namelist_use.f90

[nncarlson]

The namelist_use.f90 test adds to a namelist gotten by USE association. The test seems to acknowledge that allowing this is an extension. This violates C584 (F08) and C594 (F15).

[nncarlson]

One could argue this feature is a deliberate extension, I suppose.

[jerryd]

Would it be better to change the warning wording to say "extension" and then give an error with -std=xxxx ? or just always give an error? Disregard: I see we do give an error with -std=f95

[nncarlson]

And also with all the later -std=f2003, etc. I also dug into the options a bit and found -pedantic which does warn that is an extension. So I think there's nothing to see here.