* s/usg5-4.h (LIBS_SYSTEM): Remove, system for which this was

* s/usg5-4.h (LIBS_SYSTEM): Remove, system for which this was
added not supported anymore.

* s/usg5-4-2.h (LIBS_SYSTEM):
* s/sol2.h (LIBS_SYSTEM): Do not undefine.

* s/netbsd.h (GETPGRP_NO_ARG, N_TRELOFF):
* s/lynxos.h (GETPGRP_NO_ARG):
* s/hpux10-20.h (NO_SIOCTL_H):
* s/gnu.h (GETPGRP_NO_ARG):
* s/gnu-linux.h (NO_SIOCTL_H):
* s/freebsd.h (GETPGRP_NO_ARG, N_TRELOFF):
* s/cygwin.h (GETPGRP_NO_ARG):
* s/irix6-5.h (LIBS_SYSTEM, GETPGRP_NO_ARG): Remove, unused.
(C_DEBUG_SWITCH): Remove duplicate definition.

* m/ibms390.h: Remove boilerplate comments.

* sysdep.c (closedir): Use SOLARIS2 instead of sun && USG5_4.

* process.c (HAVE_SERIAL): Consolidate ifdefs.
(wait_reading_process_output): Remove code for SunOS, platform not
supported anymore.  Use SOLARIS2 instead of sun.