Enable getdeps build on macOS
Enable getdeps build on macOS

Summary:
Enabling Velox/f4d getpdeps build on macOS, and adding the last
required dependency (libicu).

Reviewed By: amitkdutta

Differential Revision: D27316661

fbshipit-source-id: 60edf7d4a953a62f2b7b52d9b4f0827d12ac1367

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift