improve gbuild-to-ide error message

Change-Id: Ia8986764e48f1dbe39374d511a188bd2b5f49e13
Reviewed-on: https://gerrit.libreoffice.org/11654Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

bin/gbuild-to-ide

@@ -889,7 +889,7 @@ if __name__ == '__main__':
         'debug': DebugIntegrationGenerator}
 
     if args.ide not in generators.keys():
-        parser.print_help()
+        print("Invalid ide. valid values are %s" % ','.join(generators.keys()))
         sys.exit(1)
 
     if args.input: