Adding yaml-cpp fboss code for oss
Adding yaml-cpp fboss code for oss

Summary: Added yaml-cpp library to the fboss OSS build

Reviewed By: shri-khare

Differential Revision: D25126509

fbshipit-source-id: 1e88150dbf8c96a5ac696e003265dc1f14bec105

facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman