msghandler follow-up: msdos cross-compile warnings

pline.c: In function 'execplinehandler':
pline.c:631:17: warning: unused variable 'args' [-Wunused-variable]
  631 |     const char *args[3];
      |                 ^~~~
pline.c:626:30: warning: unused parameter 'line' [-Wunused-parameter]
  626 | execplinehandler(const char *line)
      |                  ~~~~~~~~~~~~^~~~

src/pline.c

@@ -664,6 +664,8 @@ execplinehandler(const char *line)
     }
 #else
     use_pline_handler = FALSE;
+    nhUse(args);
+    nhUse(line);
 #endif
 }