Fix missing `#ifdef` in `Trace.cpp`
Fix missing `#ifdef` in `Trace.cpp`

Summary: As title.

Reviewed By: yuxuanchen1997

Differential Revision: D25542549

fbshipit-source-id: 11ad136b26165c3678a611a43fdc77e0958b9b62

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex