Summary: This diff should let us include folly/io:compression into iOS and Android projects without pulling in a lot of dependencies and should allow the use of zlib.

Test Plan: fbconfig -r folly/io/tests && fbmake runtests

Reviewed By: seanc@fb.com

Subscribers: trunkagent, bmatheny, folly-diffs@, yfeldblum, seanc, benyluo

FB internal diff: D1853058

Tasks: 6245912

Signature: t1:1853058:1424370881:2ea243d93e6041502e5e356fa430c2483f652b40