The standard is ambiguous, but we can only support
arrays/array-sections/etc of the composite type, so make sure we enforce
the rule that way. This will better support how we need to do lowering.
Brought up in a previous review as a TODO, we could be better about how
we highlight what hte previous clause was, and how to show that the
'device_type' is the one being targetted. This patch rewords the
diagnostics and updates a massive number of tests.
Once again, this is a clause on a combined construct that does almost
exactly what the loop/compute construct version does, only with some sl
ightly different evaluation rules/sema rules as it doesn't have to
consider the parent, just the 'combined' construct. The two sets of
rules for reduction on loop and compute are fine together, so this
ensures they are all enforced for this too.
The 'gangs' 'num_gangs' 'reduction' diagnostic (Dim>1) had to be applied
to num_gangs as well, as it previously wasn't permissible to get in this
situation, but we now can.
