Fix ksh hanging in pipes

Under certain conditions, ksh scripts may hang when piped through
a program that terminates before EOF.

Discussion and reproducer:
https://bugzilla.redhat.com/show_bug.cgi?id=1457990
https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01961.html

src/cmd/ksh93/sh/jobs.c:
- In job_wait(), correctly set the terminal foreground process
  group when resuming a process.

(cherry picked from commit 99ef2ca5309da91fdead74bea00743960d470c6a)

src/cmd/ksh93/sh/jobs.c

@@ -1578,6 +1578,7 @@ int	job_wait(register pid_t pid)
 					if( pw->p_exit!=SIGTTIN && pw->p_exit!=SIGTTOU)
 						break;
 
+					tcsetpgrp(JOBTTY,pw->p_pgrp);
 					killpg(pw->p_pgrp,SIGCONT);
 				}
 				else /* ignore stop when non-interactive */