Fix build without zlib compression enabled
Fix build without zlib compression enabled

Summary: The namespace alias was trying to alias a namespace that doesn't exist unless Folly is being compiled with zlib support.

Reviewed By: terrelln

Differential Revision: D5810929

fbshipit-source-id: c659d8f775fc9b99e57cc95f5914418507e546fb

facebook/folly,rklabs/folly,Orvid/folly,Orvid/folly,rklabs/folly,Orvid/folly,Orvid/folly,facebook/folly,rklabs/folly,facebook/folly,Orvid/folly,rklabs/folly,rklabs/folly,facebook/folly,facebook/folly