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/modules/mc_pos_control_multiplatform/mc_pos_control.cpp

@@ -65,7 +65,7 @@ MulticopterPositionControl::MulticopterPositionControl() :
 	_local_pos_sp_msg(),
 	_global_vel_sp_msg(),
 
-	_n(),
+	_n(_mgr),
 
 	/* parameters */
 	_params_handles({

src/modules/mc_pos_control_multiplatform/mc_pos_control.h

@@ -107,6 +107,8 @@ protected:
 
 	px4::NodeHandle _n;
 
+	px4::AppMgr _mgr;
+
 	struct {
 		px4::ParameterFloat thr_min;
 		px4::ParameterFloat thr_max;