Summary:
I want to access the list of deps without the install
instructions attached later in this stack of diffs in `shell_builder.py`.

Refs: https://github.com/facebook/watchman/pull/639

Reviewed By: snarkmaster

Differential Revision: D9552419

fbshipit-source-id: 333cfa0c33bc1aa623de7ac3546a8f1785869a4f