Update OSS CMakeLists.txt to use CMAKE_CXX_STANDARD
Update OSS CMakeLists.txt to use CMAKE_CXX_STANDARD

Summary: Adjust low level deps in OSS builds to use standard `CMAKE_CXX_STANDARD` variables to control std level in cpp builds.

Reviewed By: yfeldblum

Differential Revision: D23333713

fbshipit-source-id: cd76712d6b045f1d0aff30d4874d9bf0ce6f1e01

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