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_att_control_multiplatform/mc_att_control.cpp

@@ -71,7 +71,7 @@ MulticopterAttitudeControl::MulticopterAttitudeControl() :
 	_att_sp_pub(nullptr),
 	_v_rates_sp_pub(nullptr),
 	_actuators_0_pub(nullptr),
-	_n(),
+	_n(_mgr),
 
 	/* parameters */
 	_params_handles({

src/modules/mc_att_control_multiplatform/mc_att_control.h

@@ -94,6 +94,8 @@ private:
 
 	px4::NodeHandle _n;
 
+	px4::AppMgr _mgr;
+
 	struct {
 		px4::ParameterFloat roll_p;
 		px4::ParameterFloat roll_rate_p;