cmake fmu-v3 fix and enable more examples

- sync posix_sitl_default and px4fmu-v4pro/v5 with fmu-v3
 - fixes #6667

src/examples/px4_daemon_app/px4_daemon_app.c

@@ -44,7 +44,7 @@
 #include <unistd.h>
 
 #include <px4_config.h>
-#include <nuttx/sched.h>
+#include <px4_tasks.h>
 
 #include <systemlib/systemlib.h>
 #include <systemlib/err.h>

src/examples/rover_steering_control/main.cpp

@@ -427,7 +427,7 @@ int rover_steering_control_main(int argc, char *argv[])
 						 SCHED_PRIORITY_MAX - 20,
 						 2048,
 						 rover_steering_control_thread_main,
-						 (argv) ? (char *const *)&argv[2] : (char *const *)NULL);
+						 (argv) ? (char *const *)&argv[2] : (char *const *)nullptr);
 		thread_running = true;
 		exit(0);
 	}