FlightTask: fix CI: static field requiring definition in cpp file, errors with clang linker (CI) but not with GCC

src/lib/FlightTasks/tasks/FlightTask.cpp

@@ -1,10 +1,12 @@
 #include "FlightTask.hpp"
 #include <mathlib/mathlib.h>
 
+constexpr uint64_t FlightTask::_timeout;
+
 int FlightTask::update()
 {
 	_time = hrt_elapsed_time(&_starting_time_stamp) / 1e6f;
-	_deltatime  = math::min((int)hrt_elapsed_time(&_last_time_stamp), _timeout) / 1e6f;
+	_deltatime  = math::min(hrt_elapsed_time(&_last_time_stamp), _timeout) / 1e6f;
 	_last_time_stamp = hrt_absolute_time();
 	updateSubscriptions();
 	_evaluate_vehicle_position();

src/lib/FlightTasks/tasks/FlightTask.hpp

@@ -89,7 +89,7 @@ public:
 	};
 
 protected:
-	static constexpr int _timeout = 500000; /*< maximal time in us before a loop or data times out */
+	static constexpr uint64_t _timeout = 500000; /*< maximal time in us before a loop or data times out */
 
 	float _time = 0; /**< passed time in seconds since the task was activated */
 	float _deltatime = 0; /**< passed time in seconds since the task was last updated */