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/readproc.h

@@ -177,7 +177,9 @@ typedef struct proc_t {
         *lxcname,       // n/a             lxc container name
         *exe;           // exe             executable path + name
     int
-        luid;           // loginuid        user id at login
+        luid,           // loginuid        user id at login
+        autogrp_id,     // autogroup       autogroup number (id)
+        autogrp_nice;   // autogroup       autogroup nice value
 } proc_t;
 
 // PROCTAB: data structure holding the persistent information readproc needs
@@ -253,6 +255,9 @@ typedef struct PROCTAB {
 #define PROC_FILL_OGROUPS  ( 0x00400000 | PROC_FILLSTATUS ) // obtain other group names
 #define PROC_FILL_SUPGRP   ( 0x00800000 | PROC_FILLSTATUS ) // obtain supplementary group names
 
+// and let's put new flags here ...
+#define PROC_FILLAUTOGRP     0x01000000 // fill in proc_t autogroup stuff
+
 // it helps to give app code a few spare bits
 #define PROC_SPARE_1         0x10000000
 #define PROC_SPARE_2         0x20000000