Include the Builtins portability header in Bits.h
Include the Builtins portability header in Bits.h

Summary: Because we need it for MSVC.

Reviewed By: yfeldblum

Differential Revision: D3601138

fbshipit-source-id: 4d2ba3f9c972717745289686b025d2763f9ef30d

facebook/folly,facebook/folly,Orvid/folly,rklabs/folly,charsyam/folly,facebook/folly,floxard/folly,floxard/folly,charsyam/folly,facebook/folly,facebook/folly,rklabs/folly,Orvid/folly,Orvid/folly,charsyam/folly,floxard/folly,floxard/folly,rklabs/folly,rklabs/folly,floxard/folly,rklabs/folly,charsyam/folly,Orvid/folly,Orvid/folly