sha1dc: optionally use sha1collisiondetection as a submodule

Add an option to use the sha1collisiondetection library from the
submodule in sha1collisiondetection/ instead of in the copy in the
sha1dc/ directory.

This allows us to try out the submodule in sha1collisiondetection
without breaking the build for anyone who's not expecting them as we
work out any kinks.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 0 deletions

diff --git a/sha1collisiondetection b/sha1collisiondetection
new file mode 160000
+Subproject 19d97bf5af05312267c2e874ee6bcf584d9e968