fix memory leak in optimize pragma parsing

The optimize pragma/attribute parsing calls decode_cmdline_options_to_array
but doesn't free the array.  The following fixes that.

2021-02-10  Richard Biener  <rguenther@suse.de>

gcc/c-family/
	* c-common.c (parse_optimize_options): Free decoded_options.

gcc/c-family/c-common.c

@@ -5770,6 +5770,7 @@ parse_optimize_options (tree args, bool attr_p)
   decode_options (&global_options, &global_options_set,
 		  decoded_options, decoded_options_count,
 		  input_location, global_dc, NULL);
+  free (decoded_options);
 
   targetm.override_options_after_change();