Fix SIGHUP on termination (Solaris patch 260-22964338)

This fixes the following bug filed with Solaris: "22964338 ksh93
appears to send SIGHUP to unrelated processes on occasion". It is
fixed by applying this patch by Lijo George from the Solaris repo:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/260-22964338.patch

The ksh2020 upstream rejected this, but if it's in production use
in Solaris, Solaris, it's probably good enough for 93u+m. If any
breakage is left, it can be fixed later.
https://github.com/att/ast/pull/1

src/cmd/ksh93/include/jobs.h,
src/cmd/ksh93/sh/fault.c,
src/cmd/ksh93/sh/jobs.c:
- Use a new job_hup() function instead of job_kill() to send SIGHUP
  to job processes on termination. The new function checks if a job
  is in fact still live before issuing SIGHUP to it.

src/cmd/ksh93/include/jobs.h

@@ -179,6 +179,7 @@ extern void	job_chldtrap(Shell_t*, const char*,int);
 	extern int	job_close(Shell_t*);
 	extern int	job_list(struct process*,int);
 	extern int	job_terminate(struct process*,int);
+	extern int	job_hup(struct process *, int);
 	extern int	job_switch(struct process*,int);
 	extern void	job_fork(pid_t);
 	extern int	job_reap(int);

src/cmd/ksh93/sh/fault.c

@@ -634,7 +634,7 @@ void sh_done(void *ptr, register int sig)
 #endif
 #ifdef JOBS
 	if((sh_isoption(SH_INTERACTIVE) && shp->login_sh) || (!sh_isoption(SH_INTERACTIVE) && (sig==SIGHUP)))
-		job_walk(sfstderr,job_terminate,SIGHUP,NIL(char**));
+		job_walk(sfstderr, job_hup, SIGHUP, NIL(char**));
 #endif	/* JOBS */
 	job_close(shp);
 	if(nv_search("VMTRACE", shp->var_tree,0))

src/cmd/ksh93/sh/jobs.c

@@ -1072,6 +1072,54 @@ int job_kill(register struct process *pw,register int sig)
 	return(r);
 }
 
+/*
+ * Similar to job_kill, but dedicated to SIGHUP handling when session is
+ * being disconnected.
+ */
+int job_hup(struct process *pw, int sig)
+{
+	struct process	*px;
+	pid_t	pid;
+	int	r;
+	NOT_USED(sig);
+	if(pw->p_pgrp == 0 || (pw->p_flag & P_DISOWN))
+		return(0);
+	job_lock();
+	if(pw->p_pgrp != 0)
+	{
+		int	palive = 0;
+		for(px = pw; px != NULL; px = px->p_nxtproc)
+		{
+			if((px->p_flag & P_DONE) == 0)
+			{
+				palive = 1;
+				break;
+			}
+		}
+		/*
+		 * If all the processes have died, there is no guarantee that
+		 * p_pgrp is still the valid process group that we made, i.e.,
+		 * the PID may have been recycled and the same p_pgrp may have
+		 * been assigned to unrelated processes.
+		 */
+		if(palive)
+		{
+			if(killpg(pw->p_pgrp, SIGHUP) >= 0)
+				job_unstop(pw);
+		}
+	}
+	for(; pw != NULL && pw->p_pgrp == 0; pw = pw->p_nxtproc)
+	{
+		if(pw->p_flag & P_DONE)
+			continue;
+		if(kill(pw->p_pid, SIGHUP) >= 0)
+			(void)kill(pw->p_pid, SIGCONT);
+		pw = pw->p_nxtproc;
+	}
+	job_unlock();
+	return(0);
+}
+
 /*
  * Get process structure from first letters of jobname
  *