bin/58687: sh: implement suspend builtin

[uwe%stderr.spb.ru@localhost]

>Number:         58687
>Category:       bin
>Synopsis:       sh: implement suspend  builtin
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sun Sep 22 17:50:01 +0000 2024
>Originator:     Valery Ushakov
>Release:        NetBSD 10
>Organization:
>Environment:
>Description:
Our /bin/sh doesn't have "suspend" builtin/alias, like the one found in
ksh or bash.  Dunno, how bash implements it, but ksh e.g. simply 
predefines:

  $ alias suspend
  suspend='kill -STOP $$'

It would be nice to have it.
>How-To-Repeat:
Try to suspend a spawned shell, e.g. /bin/sh started from some other
shell to test something, or a super-user shell started by su.

>Fix: