Remove off_t typedef from cygwin/types.h thus relying on sys/types.h.
Introduce winsup/cygwin/machine/_types.h and move some types shared
with newlib into it. Get rid of their definition in cygwin/types.h.
Add same handling for __key_t/key_t as for the other types.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>