Summary:
To specify a new flag to run some test using our framework, one currently has
to add a new argument to the method that runs Infer and modify existing methods
to give a default value to that argument everywhere. With this diff, it's
possible to just specify extra arguments as parameters to
`createCInferCommand()` et al.
Reviewed By: martinoluca
Differential Revision: D3522161
fbshipit-source-id: 1499fc2