Simulator: Add missing header

src/modules/simulator/simulator_mavlink.cpp

@@ -39,6 +39,10 @@
 #include <drivers/drv_pwm_output.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
+#ifdef __PX4_LINUX
+#define _GNU_SOURCE
+#endif
+#include <pthread.h>
 
 extern "C" __EXPORT hrt_abstime hrt_reset(void);