Fix Mac build
Fix Mac build

Summary: The usual `long` vs `long long` OS X issue. This just wants to
return an `int` anyways, so let's just do that.

Reviewed By: fugalh

Differential Revision: D2596229

fb-gh-sync-id: 7f1f252553b7d1eb7a302c400b6d5d387d69ce74

Dalzhim/wangle,facebook/wangle,facebook/wangle,Dalzhim/wangle,jamperry/wangle,jamperry/wangle,facebook/wangle