Summary:
The new boost has an MSVC detection algorithm that 1) I don't
understand and 2) does not even seem deterministic. Since our internal
builds are pinned to vc142, force that in the manifest.

Reviewed By: fanzeyi

Differential Revision: D34085081

fbshipit-source-id: d8ce4d8e28aad14f6fa60f9227dafb546ce321e5