Darwin porting patches from Peter Bierman <bierman@apple.com>

src/backend/port/Makefile.in

src/backend/port/darwin/Makefile

src/backend/port/darwin/sem.c

src/backend/port/dynloader/darwin.c

src/backend/port/dynloader/darwin.h

src/backend/storage/buffer/s_lock.c

src/backend/storage/ipc/ipc.c

src/backend/storage/ipc/spin.c

src/backend/storage/lmgr/proc.c

src/include/port/darwin.h

src/include/port/darwin/sem.h

src/makefiles/Makefile.darwin

src/template/darwin