Add 'contrib/libder/' from commit '9c40c4de4c33b2ba1124fb752ebea0bebaa6013f'
git-subtree-dir: contrib/libder
git-subtree-mainline: d11904b350214943dedb64c7121d4602799d7afd
git-subtree-split: 9c40c4de4c33b2ba1124fb752ebea0bebaa6013f
(cherry picked from commit 35c0a8c449fd2b7f75029ebed5e10852240f0865)