Add 'contrib/unifdef/' from commit '0da44885831dc0a43c4ca6ff04a2430993cc0a80'

git-subtree-dir: contrib/unifdef
git-subtree-mainline: 3b7ffacdee49f90716cba2bcf8af3fc1971ae031
git-subtree-split: 0da44885831dc0a43c4ca6ff04a2430993cc0a80
(cherry picked from commit fb3ef04d2028110f06d68b09009f1f2ca0f4128e)

unifdef: Reapply our 61287be18189.

(cherry picked from commit 343b776fd0280f4dc95a1a61fd9ac40c78ce684e)

unifdef: Reapply our 7102ec5226e5.

(cherry picked from commit 049b7608f41bf4e93ac6de718c45bef261f6977d)