Cygwin: Don't change pgid to ctty pgid under debugger

_pinfo::set_ctty sets myself's pgid to the ctty pgid if the process has
been started from a non-Cygwin process.  This isn't the right thing to
do when started from GDB.  GDB starts the application via standard
Windows means, not via Cygwin fork/exec, so it's treated as being
a non-Cygwin parent.

But we want the app running in it's own process group.  So skip this
step when running under a debugger

Signed-off-by: Corinna Vinschen <corinna-cygwin@cygwin.com>

winsup/cygwin/pinfo.cc

@@ -554,7 +554,11 @@ _pinfo::set_ctty (fhandler_termios *fh, int flags)
       syscall_printf ("attaching %s sid %d, pid %d, pgid %d, tty->pgid %d, tty->sid %d",
 		      __ctty (), sid, pid, pgid, tc.getpgid (), tc.getsid ());
       if (!cygwin_finished_initializing && !myself->cygstarted
-	  && pgid == pid && tc.getpgid () && tc.getsid ())
+	  && pgid == pid && tc.getpgid () && tc.getsid ()
+	  /* Even GDB starts app via CreateProcess which changes cygstarted.
+	     This results in setting the wrong pgid here, so just skip this
+	     under debugger. */
+	  && !being_debugged ())
 	pgid = tc.getpgid ();
 
       /* May actually need to do this: