sha1: move the sha1collisiondetection code to third-party
Move the third-party sha1collisiondetection code from clib/sha1 to
third-party/sha1dc. This helps isolate third-party code from our own
internally developed code.
This also updates the code to use the same include paths and library names as
used by the sha1collisiondetection's upstream Makefile, which would be needed
to link against a version of sha1collisiondetection installed locally.
Confirmed "make local" succeeds.
All of the tests pass, except for test-check-commit-hg, which complains about
the fact that some of this third-party code contains multiple empty lines in a
row. It doesn't seem straightforward to update test-check-commit to ignore
this third-party code, but these test failures shouldn't affect any future
Reviewers: #fbhgext, ryanmce
Reviewed By: #fbhgext, ryanmce
Differential Revision: https://phab.mercurial-scm.org/D281