[flang] Fix check for assumed-size arguments to SHAPE() & al.

[klausler]

Summary

The predicate that is used to detect an invalid assumed-size argument
to the intrinsic functions SHAPE, SIZE, & LBOUND gives false results
for arguments whose shapes are not calculatable at compilation time.
Replace with an explicit test for an assumed-size array dummy argument
symbol.

[jeanPerier]

LGTM

flang/lib/Evaluate/intrinsics.cpp

if (const ActualArgument * arg{actualForDummy[j]}) {
                 std::strcmp(name, "size") == 0 ||
                 std::strcmp(name, "ubound") == 0)) {
           // Check for an assumed-size array argument.
           // These are disallowed for SHAPE, and require DIM= for
           // SIZE and UBOUND.
           // (A previous error message for UBOUND will take precedence
           // over this one, as this error is caught by the second entry
           // for UBOUND.)
-          if (std::optional<Shape> shape{GetShape(context, *arg)}) {
-            if (!shape->empty() && !shape->back().has_value()) {
+          if (const Symbol * argSym{GetLastSymbol(*arg)}) {
+            if (semantics::IsAssumedSizeArray(*argSym)) {
               if (strcmp(name, "shape") == 0) {
                 messages.Say(arg->sourceLocation(),
                     "The '%s=' argument to the intrinsic function '%s' may not be assumed-size"_err_en_US,
                     d.keyword, name);
               } else {
                 messages.Say(arg->sourceLocation(),
                     "A dim= argument is required for '%s' when the array is assumed-size"_err_en_US,
                     name);