update TimeUtil to use getOSThreadID()
update TimeUtil to use getOSThreadID()

Summary:
Use the newly introduced getOSThreadID() function to get a thread ID for
determining thread scheduling information on Linux.

Reviewed By: yfeldblum

Differential Revision: D5173596

fbshipit-source-id: 3e6fa352c3774986b0ac1f93bd6c7e4a29e08471

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