Don't give an error when format string is not a string literal.

This may be indicative of dubious code in some cases, but it can also have valid use cases that are not easy to modify.

If desired, this could be re-enabled under a separate lint flag (analogous to -Wformat-nonliteral in GCC/Clang, which is available as an option but is not included in -Wformat or -Wall).

Printf.pas

@@ -860,7 +860,7 @@ var
       if (tk <> nil) and (tk^.token.kind = stringconst) then
          get_format_string := tk^.token.sval
       else
-         Error(125);
+         {Error(125) - disabled for now};
       end; {if}
       { no format string -> Error(85) }
    end; {get_format_string}