[flang] Silence inappropriate error message (#120614)

A recent patch added better compatibility checking for actual procedure
arguments, but it has led to a few failures in the Fujitsu Fortran test
suite in cases of NULL() actual arguments being associated with dummy
procedure pointers. As is the case with dummy data pointers, these must
always be accepted.

Fixes Fujitsu Fortran test cases 0249_0023 through 0028 and 0387_0047.

Author: klausler

flang/lib/Semantics/expression.cpp

@@ -2536,6 +2536,15 @@ static bool CheckCompatibleArgument(bool isElemental,
             return false;
           },
           [&](const characteristics::DummyProcedure &dummy) {
+            if ((dummy.attrs.test(
+                     characteristics::DummyProcedure::Attr::Optional) ||
+                    dummy.attrs.test(
+                        characteristics::DummyProcedure::Attr::Pointer)) &&
+                IsBareNullPointer(expr)) {
+              // NULL() is compatible with any dummy pointer
+              // or optional dummy procedure.
+              return true;
+            }
             if (!expr || !IsProcedurePointerTarget(*expr)) {
               return false;
             }