Abstractions to compile systemlib for Linux and Nuttx

Modified uint32_t casts of pointers to unsigned long for portability.
It otherwise breaks on x86_64.

Added _PX4_IOC to handle the conflice between _IOC on Linux and NuttX.

Removed use of px4::ok() because it cannot be used in a thread based
implementation. Changed to use px4::AppMgr which uses ok() on ROS.

Removed up_cxxinitialize.c from Linux build.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/examples/publisher/publisher_example.cpp

@@ -44,7 +44,7 @@
 using namespace px4;
 
 PublisherExample::PublisherExample() :
-	_n(),
+	_n(mgr),
 	_rc_channels_pub(_n.advertise<px4_rc_channels>()),
 	_v_att_pub(_n.advertise<px4_vehicle_attitude>()),
 	_parameter_update_pub(_n.advertise<px4_parameter_update>())
@@ -55,7 +55,7 @@ int PublisherExample::main()
 {
 	px4::Rate loop_rate(10);
 
-	while (px4::ok()) {
+	while (!mgr.exitRequested()) {
 		loop_rate.sleep();
 		_n.spinOnce();