[flang] Add TODO when trying to do a polymorphic temp in getTempExtAddr

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D144459

Author: clementval

flang/lib/Lower/ConvertExpr.cpp

@@ -2021,6 +2021,8 @@ class ScalarExprLowering {
         },
         [&](const fir::BoxValue &x) -> ExtValue {
           // Derived type scalar that may be polymorphic.
+          if (fir::isPolymorphicType(fir::getBase(x).getType()))
+            TODO(loc, "polymorphic array temporary");
           assert(!x.hasRank() && x.isDerived());
           if (x.isDerivedWithLenParameters())
             fir::emitFatalError(