Definitions of ETC_GITCONFIG, ETC_GITATTRIBUTES and sysconfdir depend on
value of prefix. As prefix can be changed in config.mak.autogen, all if
blocks with conditions based on prefix should be placed after the file
is included in Makefile.
Signed-off-by: Kacper Kornet <draenog@pld-linux.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>