Give an appropriate error for an illegal operator in a constant expression.

This was being reported as an "illegal type cast".

Expression.pas

@@ -2163,7 +2163,7 @@ if token.kind in startExpression then begin
                       and (token.kind = sizeofsy))
                   or ((kind <> initializerExpression)
                       and (token.kind = uand)) then begin
-                  Error(40);
+                  Error(161);
                   errorFound := true;
                   end; {if}
             if token.kind in         {make sure we get what we want}

Scanner.pas

@@ -714,6 +714,7 @@ if list or (numErr <> 0) then begin
         158: msg := @'_Generic expression includes two compatible types';
         159: msg := @'_Generic expression includes multiple default cases';
         160: msg := @'no matching association in _Generic expression';
+        161: msg := @'illegal operator in a constant expression';
          otherwise: Error(57);
          end; {case}
        writeln(msg^);

cc.notes

@@ -1196,6 +1196,8 @@ int foo(int[42]);
 
 157. An error was not reported if code tried to define an enumeration constant with a value in the range 0xFFFF8000 to 0xFFFFFFFF.  (Enumeration constants are limited to values representable as an int.)
 
+158. An "illegal type cast" error would be reported when an illegal operator was used in a constant expression.  An appropriate error message is now produced.
+
 -- Bugs from C 2.1.0 that have been fixed -----------------------------------
 
 1.  In some situations, fread() reread the first 1K or so of the file.