Move ThreadName.cpp macro defs outside C++ section
Move ThreadName.cpp macro defs outside C++ section

Summary: [Folly] Move `ThreadName.cpp` macro defs outside C++ section, including outside `namespace ...` blocks.

Reviewed By: vitaut

Differential Revision: D17868541

fbshipit-source-id: a0964ce1f1c6322185f94b8162df4c0e6eaa84bf

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