There are two very similar blocks of code that recognize options for
the "recursive" merge strategy. Unify them.
No functional change intended.
Cc: Avery Pennarun <apenwarr@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>