Allow NO_GECOS_IN_PWENT to be defined in the Makefile for platforms that
lack the pw_gecos field in their "struct passwd", in which case the
uppercased user name is used instead via the standard '&' replacement
mechanism.
Signed-off-by: Rafael Gieschke <rafael@gieschke.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>