Fix FreeBSD Build for Huge Page Allocator
Fix FreeBSD Build for Huge Page Allocator

Summary:
I don't really understand how FreeBSD allocates huge pages. There doesn't seem
to be any explicit mechanism to ask for them, other than `MAP_ALIGNED_SUPER`
which should just make the allocation aligned correctly? At any rate, this
should build and return FreeBSD to basically the way it worked before.

Fixes #1622.

Reviewed By: davidtgoldblatt

Differential Revision: D29915224

fbshipit-source-id: 9c5973714bd6ad3d1f0c6f3969ccdd23f17114e7

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly