Building /tmp/ArduCopter.build/ArduCopter.elf
%% ArduCopter.elf
/tmp/ArduCopter.build/libraries/AC_PrecLand/AC_PrecLand_IRLock.o: In function ZN18AC_PrecLand_IRLock4initEv': /home/hussein/ardupilot/libraries/AC_PrecLand/AC_PrecLand_IRLock.cpp:21: undefined reference toAP_IRLock_PX4::init()’
/tmp/ArduCopter.build/libraries/AC_PrecLand/AC_PrecLand_IRLock.o: In function ZN18AC_PrecLand_IRLock6updateEv': /home/hussein/ardupilot/libraries/AC_PrecLand/AC_PrecLand_IRLock.cpp:31: undefined reference toAP_IRLock_PX4::update()’
/tmp/ArduCopter.build/libraries/AC_PrecLand/AC_PrecLand_IRLock.o: In function ZN13AP_IRLock_PX4D4Ev': /home/hussein/ardupilot/libraries/AP_IRLock/AP_IRLock_PX4.h:11: undefined reference tovtable for AP_IRLock_PX4’
/home/hussein/ardupilot/libraries/AP_IRLock/AP_IRLock_PX4.h:11: undefined reference to vtable for AP_IRLock_PX4' /tmp/ArduCopter.build/libraries/AC_PrecLand/AC_PrecLand_IRLock.o: In functionZN18AC_PrecLand_IRLockC2ERK11AC_PrecLandRNS0_14precland_stateE’:
/home/hussein/ardupilot/libraries/AC_PrecLand/AC_PrecLand_IRLock.cpp:14: undefined reference to `AP_IRLock_PX4::AP_IRLock_PX4()'
collect2: error: ld returned 1 exit status
make: *** [D:/cygwin/home/hussein/ardupilot/mk/board_native.mk:131: /tmp/ArduCopter.build/ArduCopter.elf] Error 1