Support __builtin_popcountl on Windows
Support __builtin_popcountl on Windows

Summary: Because Bits.h feels the need to exercise all variants of popcount.

Reviewed By: yfeldblum

Differential Revision: D9565298

fbshipit-source-id: 307b3e4a70216c76d63104853e91e36a340ff1ab

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