SITL: use PACKED attribute in fdm structure

libraries/SITL/SITL.h

@@ -8,8 +8,7 @@
 #include <AP_Math.h>
 #include <GCS_MAVLink.h>
 
-#pragma pack(push,1)
-struct sitl_fdm {
+struct PACKED sitl_fdm {
 	// this is the packet sent by the simulator
 	// to the APM executable to update the simulator state
 	// All values are little-endian
@@ -23,7 +22,6 @@ struct sitl_fdm {
 	double airspeed; // m/s
 	uint32_t magic; // 0x4c56414f
 };
-#pragma pack(pop)
 
 
 class SITL