[Patch, Fortran + Testsuite] Fix coarray handling in modules

[FX]

> As found by Alessandro: Statically allocated coarrays in declared in the specification part of a module didn't work (link-time failure). The reason was that the associated coarray token was wrongly mangled and not a public tree.
> 
> I additionally propagated the dg-compile-aux-modules support to caf.dg (currently unused).

OK. It’s probably best to commit the two parts as separate commits, though.

FX