This is zlib 1.2.11.

It can be downloaded from http://www.zlib.net , or, equivalently, from
http://github.com/madler/zlib .

The commit hash on Github is https://github.com/madler/zlib/commit/cacf7f1d4e3d44d871b605da3b647f07d718623f.
`LICENSE.txt` is copy-pasted from `zlib.h` and a simple `BUILD` file is added.