Summary:
This removes the old way of consuming `libfolly_runtime.so` from
`Android-prebuilt.cmake` to using Prefab which is natively supported
by the Android pipeline.
Moreover, I've exposed a `folly-flags.cmake` file which can be used by libraries
to know which lists of flags they need to use for Folly.
Changelog:
[Internal] [Changed] - Move `folly_runtime` to be consumed via prefab
Reviewed By: cipolleschi
Differential Revision: D39928571
fbshipit-source-id: 4864c37813ec681a6a464c97de6dfc078f5553f1
Nicola Corti