* syscalls.cc: Include utmpx.h. Implement utmpx functions as stubs
to utmp functions.
(copy_ut_to_utx): New static function.
(pututline): Change from void to struct utmp * as on Linux.
(setutxent): New function.
(endutxent): New function.
(getutxent): New function.
(getutxid): New function.
(getutxline): New function.
(pututxline): New function.
* include/utmpx.h: New file.
* include/cygwin/utmp.h: New file.
* include/cygwin/version.h: Bump API minor number.
* include/sys/utmp.h: Include cygwin/utmp.h. Move stuff common with
utmpx functionality there.
(pututline): Declare struct utmp *.
