[flang] Don't emit conversion error for max(a,b, optionalCharacter) (#88156)

A recent patch added an error message for whole optional dummy argument
usage as optional arguments (third or later) to MAX and MIN when those
names required type conversion, since that conversion only works when
the optional arguments are present. This check shouldn't care about
character lengths. Make it so.

Author: klausler

flang/lib/Semantics/check-call.cpp

@@ -1477,10 +1477,15 @@ static void CheckMaxMin(const characteristics::Procedure &proc,
         if (arguments[j]) {
           if (const auto *expr{arguments[j]->UnwrapExpr()};
               expr && evaluate::MayBePassedAsAbsentOptional(*expr)) {
-            if (auto thisType{expr->GetType()};
-                thisType && *thisType != typeAndShape->type()) {
-              messages.Say(arguments[j]->sourceLocation(),
-                  "An actual argument to MAX/MIN requiring data conversion may not be OPTIONAL, POINTER, or ALLOCATABLE"_err_en_US);
+            if (auto thisType{expr->GetType()}) {
+              if (thisType->category() == TypeCategory::Character &&
+                  typeAndShape->type().category() == TypeCategory::Character &&
+                  thisType->kind() == typeAndShape->type().kind()) {
+                // don't care about lengths
+              } else if (*thisType != typeAndShape->type()) {
+                messages.Say(arguments[j]->sourceLocation(),
+                    "An actual argument to MAX/MIN requiring data conversion may not be OPTIONAL, POINTER, or ALLOCATABLE"_err_en_US);
+              }
             }
           }
         }