Archlinux support

This adds support for Arch Linux/Arch Linux ARM. It has been around in my repo for a long time now, with a good number of users I believe, and rarely has issues.

First 3 commits are not directly related to arch, but necessary (especially the last 2).
Evidently arch never needs stuff for compilation; I'm assuming that's because it always has the headers in the packages.

In that case, it'd be cleaner to modify compile to ignore deps on arch, instead of having to manually mask out each dependency on every call to compile.