As a follow-up to 60d24dd25 (Makefile: fold XDIFF_H and VCSSVN_H into
LIB_H), let the unconditional additions to LIB_H form a single sorted
list. Also drop the duplicate entry for xdiff/xdiff.h, which was easy
to spot after sorting.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>