Summary:
This adds a SHA1 implementation taken from public domain code.
The change is trivial, but as it involves third-party code I'd like
a second pair of eyes before commit.
LibFuzzer can not use SHA1 from openssl because openssl may not be available
and because we may be fuzzing openssl itself.
Using sha1sum via a pipe is too slow.
Test Plan: n/a
Reviewers: chandlerc
Reviewed By: chandlerc
Subscribers: majnemer, llvm-commits
Differential Revision: http://reviews.llvm.org/D9733
llvm-svn: 237400
