Update sha1dc from the latest version by the upstream
maintainer[1].

This version includes a commit of mine which allows for replacing the
local modifications done to the upstream files in git.git with macro
definitions to monkeypatch it in place.

It also brings in a change[2] upstream made for the breakage 2.13.0
introduced on SPARC and other platforms that forbid unaligned
access[3].

This means that the code customizations done since the initial import
in commit 28dc98e3 ("sha1dc: add collision-detecting sha1
implementation", 2017-03-16) can be done purely via Makefile
definitions and by including the content of our own sha1dc_git.[ch] in
sha1dc/sha1.c via a macro.

1. https://github.com/cr-marcstevens/sha1collisiondetection/commit/cc465543b310e5f59a1d534381690052e8509b22
2. https://github.com/cr-marcstevens/sha1collisiondetection/commit/33a694a9ee1b79c24be45f9eab5ac0e1aeeaf271
3. "Git 2.13.0 segfaults on Solaris SPARC due to DC_SHA1=YesPlease
   being on by default"
   (https://public-inbox.org/git/CACBZZX6nmKK8af0-UpjCKWV4R+hV-uk2xWXVA5U+_UQ3VXU03g@mail.gmail.com/)
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>