Reorganize implementation of Flist_system_processes and

Reorganize implementation of Flist_system_processes and
Fsystem_process_attributes.  No functional changes.
* process.c: Don't #include pwd.h, grp.h and limits.h.
(Flist_system_processes): Just call list_system_processes.
(Fsystem_process_attributes): Just call system_process_attributes.
(procfs_list_system_processes, time_from_jiffies)
(ltime_from_jiffies, get_up_time, procfs_ttyname, MAJOR, MINOR)
(procfs_get_total_memory, procfs_system_process_attributes): Move ...

* sysdep.c: ... here.  Include pwd.h, grp.h and limits.h.
(list_system_processes): Rename from
procfs_list_system_processes.  Enclose in #ifdef HAVE_PROCFS.
Provide a do nothing implementation.
(system_process_attributes): Rename from
procfs_list_system_processes.
(ltime_from_jiffies, get_up_time, procfs_ttyname, MAJOR, MINOR)
(procfs_get_total_memory):  Enclose in #ifdef GNU_LINUX.

* w32.c (list_system_processes): Rename from
w32_list_system_processes.
(system_process_attributes): Rename from
w32_system_process_attributes.

* s/gnu-linux.h (LISTPROC, PROCATTR): Remove.

* process.h (w32_list_system_processes)
(w32_system_process_attributes): Remove.
(list_system_processes, system_process_attributes): New
prototypes.

* config.nt (LISTPROC, PROCATTR): Remove.