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/subscriber/subscriber_example.cpp

@@ -49,7 +49,7 @@ void rc_channels_callback_function(const px4_rc_channels &msg)
 }
 
 SubscriberExample::SubscriberExample() :
-	_n(),
+	_n(_mgr),
 	_p_sub_interv("SUB_INTERV", PARAM_SUB_INTERV_DEFAULT),
 	_p_test_float("SUB_TESTF", PARAM_SUB_TESTF_DEFAULT)
 {

src/examples/subscriber/subscriber_example.h

@@ -51,12 +51,14 @@ public:
 	~SubscriberExample() {};
 
 	void spin() {_n.spin();}
+
 protected:
 	px4::NodeHandle _n;
 	px4::ParameterInt _p_sub_interv;
 	px4::ParameterFloat _p_test_float;
 	px4::Subscriber<px4_rc_channels> *_sub_rc_chan;
 
+	AppMgr _mgr;
 
 	void rc_channels_callback(const px4_rc_channels &msg);
 	void vehicle_attitude_callback(const px4_vehicle_attitude &msg);