An implied DO loop in an array constructor may not have a type (explicit
or otherwise) with a character length that depends on a value of an
implied DO index or a non-constant expression if the implied DO loop
executes no iterations. When the iteration count can be known to be
zero at compilation time, catch the case of a non-constant length
expression correctly.
Differential Revision: https://reviews.llvm.org/D156753
F'2023 7.8 para 5 requires that an implied DO loop with no iterations
in a character array constructor should have items whose lengths are
constant expressions independent of the value of the implied DO loop
index.
Differential Revision: https://reviews.llvm.org/D155968
