mavsdk_tests: build should be independant of px4

platforms/posix/cmake/sitl_target.cmake

@@ -45,6 +45,18 @@ ExternalProject_Add(sitl_gazebo
 	BUILD_ALWAYS 1
 )
 
+ExternalProject_Add(mavsdk_tests
+	SOURCE_DIR ${PX4_SOURCE_DIR}/test/mavsdk_tests
+	CMAKE_ARGS
+		-DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
+	BINARY_DIR ${PX4_BINARY_DIR}/mavsdk_tests
+	INSTALL_COMMAND ""
+	USES_TERMINAL_CONFIGURE true
+	USES_TERMINAL_BUILD true
+	EXCLUDE_FROM_ALL true
+	BUILD_ALWAYS 1
+)
+
 # create targets for each viewer/model/debugger combination
 set(viewers none jmavsim gazebo)
 set(debuggers none ide gdb lldb ddd valgrind callgrind)