Support multi-config platforms when finding gmock
Support multi-config platforms when finding gmock

Summary: This should fix running tests in a vcpkg environment.

Reviewed By: yfeldblum

Differential Revision: D7822368

fbshipit-source-id: a549febeb0bbea7208386cbed8a6ecb316b98661

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