turn on -Werror and fix resulting errors

src/modules/commander/commander.cpp

@@ -267,7 +267,7 @@ int commander_main(int argc, char *argv[])
 					     SCHED_PRIORITY_MAX - 40,
 					     3200,
 					     commander_thread_main,
-					     (argv) ? (const char **)&argv[2] : (const char **)NULL);
+					     (argv) ? (char * const *)&argv[2] : (char * const *)NULL);
 
 		while (!thread_running) {
 			usleep(200);

src/modules/commander/module.mk

@@ -51,3 +51,5 @@ SRCS		 	= commander.cpp \
 MODULE_STACKSIZE = 1200
 
 MAXOPTIMIZATION	 = -Os
+
+EXTRACXXFLAGS = -Wno-error