Support folly::getCurrentThreadID() without PThread
Support folly::getCurrentThreadID() without PThread

Summary: Just use the native Windows API call instead, as it gives the same result.

Reviewed By: yfeldblum

Differential Revision: D4887587

fbshipit-source-id: adbfd288bea425f1aff46d0685083807490f7f09

Orvid/folly,rklabs/folly,facebook/folly,facebook/folly,Orvid/folly,Orvid/folly,rklabs/folly,rklabs/folly,facebook/folly,Orvid/folly,facebook/folly,rklabs/folly,Orvid/folly,rklabs/folly,facebook/folly