revision.o is included in libgit.a which is in $(GITLIBS), so we don't
need to include is separately. This fixes compilation with
"-fwhole-program" which otherwise fails with messages like this:
libgit.a(revision.o): In function `mark_tree_uninteresting':
/home/john/src/git/revision.c:108: multiple definition of `mark_tree_uninteresting'
/tmp/ccKQRkZV.ltrans2.ltrans.o:/home/john/src/git/revision.c:108: first defined here
Signed-off-by: John Keeping <john@keeping.me.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>