switch to netbsd <sys/errno.h>

not entirely clean; _SIGN hack remains for now.  also leave in
minix-specific stuff like minix-specific errno's and OK.

Change-Id: I035efc52e27b92f58ae0d88dab19dec263edb6e3

drivers/tty/tty.c

@@ -715,6 +715,7 @@ static int do_ioctl(devminor_t minor, unsigned long request, endpoint_t endpt,
 	break;
 
     case TIOCSCTTY:
+	/* Process sets this tty as its controlling tty */
 	tp->tty_pgrp = user_endpt;
 	break;