[posix-app] include <util.h> on darwin target for forkpty (#3030)
[posix-app] include <util.h> on darwin target for forkpty (#3030)


srickardti/openthread,librasungirl/openthread,abtink/openthread,LeZhang2016/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,erja-gp/openthread,LeZhang2016/openthread,LeZhang2016/openthread,abtink/openthread,lanyuwen/openthread,bukepo/openthread,erja-gp/openthread,lanyuwen/openthread,jwhui/openthread,openthread/openthread,abtink/openthread,bukepo/openthread,librasungirl/openthread,chshu/openthread,turon/openthread,gandreello/openthread,srickardti/openthread,gandreello/openthread,LeZhang2016/openthread,bukepo/openthread,chshu/openthread,chshu/openthread,gandreello/openthread,erja-gp/openthread,jwhui/openthread,chshu/openthread,gandreello/openthread,gandreello/openthread,turon/openthread,librasungirl/openthread,librasungirl/openthread,bukepo/openthread,erja-gp/openthread,srickardti/openthread,lanyuwen/openthread,openthread/openthread,LeZhang2016/openthread,LeZhang2016/openthread,gandreello/openthread,lanyuwen/openthread,chshu/openthread,erja-gp/openthread,lanyuwen/openthread,chshu/openthread,turon/openthread,abtink/openthread,jwhui/openthread,openthread/openthread,erja-gp/openthread,turon/openthread,lanyuwen/openthread