Enable -Wwrite-strings

Also, fix leak from ztest_global_vars_to_zdb_args()

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13348

module/icp/algs/modes/gcm.c

@@ -907,7 +907,7 @@ gcm_impl_init(void)
 }
 
 static const struct {
-	char *name;
+	const char *name;
 	uint32_t sel;
 } gcm_impl_opts[] = {
 		{ "cycle",	IMPL_CYCLE },