folly: define FOLLY_SANITIZE_THREAD convenience macro for TSAN
folly: define FOLLY_SANITIZE_THREAD convenience macro for TSAN

Summary:
This defines the macro `FOLLY_SANITIZE_THREAD`, similar to `FOLLY_SANITIZE_ADDRESS`.

Note that gcc *just* landed support for the `__SANITIZE_THREAD__` macro two weeks
ago: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64354

Reviewed By: igorsugak

Differential Revision: D3389021

fbshipit-source-id: df6497a7741657c297ee812ed07cbae102b6810d

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