Patch Arcanist to check XDG config dirs for existing configs
Summary: I attempted to get this behavior upstreamed, but the devs didn't want additional complexity. With this patch, the default behavior of Arcanist does not change, but the tool will properly detect a pre-existing config file at ~/.config/arcrc or $XDG_CONFIG_DIR/arcrc, just like Git's approach to XDG Base Directory Specification compliance. This allows perfect backwards compatibility, while adding flexibility for those who don't wish to have cluttered home directories.
Test Plan: Submit this patch with a config file in ~/.config/arcrc
Reviewers: Triage Team, JoshStrobl
Reviewed By: Triage Team, JoshStrobl
Differential Revision: https://dev.getsol.us/D9353