brace-initialize common invocables
brace-initialize common invocables

Summary: Not sure if necessary today, but some compilers have historically required this.

Differential Revision: D33992255

fbshipit-source-id: 14cec23d7e6d29f7f15934e27b004f002cac71ef

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