library: add provision for displaying autogroup values

In the link referenced below there's an explanation of
the linux autogroup feature which has been around ever
since linux-2.6.38. With that explanation there's also
surprising (maybe shocking) revelations about the nice
and renice commands if CONFIG_SCHED_AUTOGROUP was set.

When autogroups are active, such programs are rendered
mostly useless because the nice value will only affect
scheduling priority relative to other processes in the
same autogroup. In order to accomplish what we thought
of as renice, that nice value in /proc/<pid>/autogroup
must be changed. Altering any single member of a group
will also affect every other member of that autogroup.

So, this commit will set the stage for users of newlib
to display autogroup identifiers plus their associated
nice values (now that their importance is understood).

Reference(s):
https://github.com/nlburgin/reallynice

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/pids.h

@@ -37,6 +37,8 @@ enum pids_item {
     PIDS_ADDR_CURR_EIP,     //   ul_int        stat: eip
     PIDS_ADDR_CURR_ESP,     //   ul_int        stat: esp
     PIDS_ADDR_STACK_START,  //   ul_int        stat: start_stack
+    PIDS_AUTOGRP_ID,        //    s_int        autogroup
+    PIDS_AUTOGRP_NICE,      //    s_int        autogroup
     PIDS_CGNAME,            //      str        derived from CGROUP ':name='
     PIDS_CGROUP,            //      str        cgroup
     PIDS_CGROUP_V,          //     strv        cgroup, as *str[]