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

See commit a0103914 ("sha1dc: update from upstream", 2017-05-20) for
the latest update. That update was done sans some whitespace changes
by upstream, which is why the diff here isn't the same as the upstream
cc46554..e139984.

It also brings in a change[2] upstream made which should hopefully
address the breakage in 2.13.1 on Cygwin, see [3]. Cygwin defines both
_BIG_ENDIAN and _LITTLE_ENDIAN.

Adam Dinwoodie reports on the mailing list that that upstream commit
fixes the issue on Cygwin[4].

1. https://github.com/cr-marcstevens/sha1collisiondetection/commit/e1399840b501a68ac6c8d7ed9a5cb1455480200e
2. https://github.com/cr-marcstevens/sha1collisiondetection/commit/a24eef58c0684078405f8c7a89f9b78271432005
3. <20170606100355.GC25777@dinwoodie.org> (https://public-inbox.org/git/20170606100355.GC25777@dinwoodie.org/)
4. <20170606124323.GD25777@dinwoodie.org> (https://public-inbox.org/git/20170606124323.GD25777@dinwoodie.org/)
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>