Fixing opt-asan/ubsan fail for folly contbuild
Fixing opt-asan/ubsan fail for folly contbuild

Summary: Flag caused compilation error on unused param, asserts optimized out in opt-asan/ubsan builds.  Replaced with DCHECK as per meyering's advice.

Reviewed By: meyering

Differential Revision: D5246089

fbshipit-source-id: dc0abda91f900dd98af31410f4667c52404997f5

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