[flang] Catch nasty order-of-declarations case (#71881)

It is possible to declare the rank of an object after that object has
been used in the same specification part in a specification function
reference whose result or generic resolution may well have depended on
the object being apparently a scalar.

Catch this case, and emit a warning -- not an error, yet, due to fear of
false positives.

See the new test for examples.