Add 'contrib/libdiff/' from commit '9eb461aa4b61ab47855b2cee9e5b626a76888b5e'
git-subtree-dir: contrib/libdiff
git-subtree-mainline: f6d489f402c320f1a6eaa473491a0b8c3878113e
git-subtree-split: 9eb461aa4b61ab47855b2cee9e5b626a76888b5e
Reviewed by: imp
Sponsored by: Klara, Inc.