READ(CVAR)[,item-list] with a character variable CVAR
could be parsed as an unformatted READ from an internal
unit or as a formatted READ from the default external unit
with a needlessly parenthesized variable format. We parse
it as the former, but Fortran doesn't have unformatted
internal I/O.
Differential revision: https://reviews.llvm.org/D90493
Rolls up small changes across the frontend to prepare for the large
forthcoming patch (part 4/4) that completes DATA statement processing
via conversion to initializers.
Reviewed By: PeteSteinfeld
Differential Revision: https://reviews.llvm.org/D82137