Import libcbor at 'contrib/libcbor/'
git-subtree-dir: contrib/libcbor
git-subtree-mainline: 293663f4da9e8b8aeb106ce3b73a8ed2aa2a8a90
git-subtree-split: 5b2defbd2a1aa991bd0a2855eef8e15107572747
(cherry picked from commit 10ff414c14eef433d8157f0c17904d740693933b)