Summary:
We would like to build a shared library with all fbcode dependencies statically linked within.
This resulting .so should not drop any symbols definitions in the building process.
To ensure that, we use `link_whole=True` according to
https://buck.build/rule/cxx_library.html#link_whole.
Since `link_whole` is `False` by default, adding a `link_whole=False` to existing libraries won't
change any behavior.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7466

Test Plan: build a .so and test internally.

Reviewed By: pdillinger

Differential Revision: D24009780

Pulled By: riversand963

fbshipit-source-id: d18804d495da7195ed72a2040e1a5de4fd336519