ParseXS: improve an error message

For the specific case of RETVAL appearing in an OUTPUT section when
NO_OUTPUT is in force, output this new more specific error message:

    can't use RETVAL in OUTPUT when NO_OUTPUT declared

rather than the more generic (and in this case, slightly confusing)
message:

    OUTPUT RETVAL not a parameter

Author: iabyn

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm

@@ -2119,11 +2119,14 @@ sub OUTPUT_handler {
       next;
     }
 
+    if ($outarg eq "RETVAL" and $self->{xsub_seen_NO_OUTPUT}) {
+      $self->blurt("Error: can't use RETVAL in OUTPUT when NO_OUTPUT declared");
+      next;
+    }
+
     if (   !$param  # no such param or, for RETVAL, RETVAL was void
-        or ($outarg eq "RETVAL"
-               ? $self->{xsub_seen_NO_OUTPUT} # mustn't return in this case
-               : !$param->{arg_num}) # not bound to an arg which can be updated
-       )
+           # not bound to an arg which can be updated
+        or $outarg ne "RETVAL" && !$param->{arg_num})
     {
       $self->blurt("Error: OUTPUT $outarg not a parameter");
       next;

dist/ExtUtils-ParseXS/t/001-basic.t

@@ -2418,7 +2418,7 @@ EOF
                 |   OUTPUT:
                 |      RETVAL
 EOF
-            [ 1, 0, qr/Error: OUTPUT RETVAL not a parameter/,  "OUTPUT err" ],
+            [ 1, 0, qr/Error: can't use RETVAL in OUTPUT when NO_OUTPUT declared/,  "OUTPUT err" ],
         ],
 
         [
@@ -2429,7 +2429,7 @@ EOF
                 |   OUTPUT:
                 |      RETVAL
 EOF
-            [ 1, 0, qr/Error: OUTPUT RETVAL not a parameter/,  "OUTPUT err" ],
+            [ 1, 0, qr/Error: can't use RETVAL in OUTPUT when NO_OUTPUT declared/,  "OUTPUT err" ],
         ],
 
         [
@@ -2442,7 +2442,7 @@ EOF
                 |   OUTPUT:
                 |      RETVAL
 EOF
-            [ 1, 0, qr/Error: OUTPUT RETVAL not a parameter/,  "OUTPUT err" ],
+            [ 1, 0, qr/Error: can't use RETVAL in OUTPUT when NO_OUTPUT declared/,  "OUTPUT err" ],
         ],