makechrootpkg: Reopen console to assign the CTTY

nspawn does not give us a controlling terminal, hence we ignore
interrupts. Apparently this was lost in systemd at some point.

Hack around this by reopening the console to make it the controlling
terminal.

makechrootpkg.in

@@ -241,6 +241,9 @@ EOF
 # These functions aren't run in makechrootpkg,
 # so no global variables
 _chrootbuild() {
+	# Work around nspawn not giving us a ctty
+	exec </dev/console
+
 	# No coredumps
 	ulimit -c 0