WIP: Better Android support

Currently a work-in-progress, but feedback is still nice. The current "fix the world" commit will be broken into smaller, logical chunks (first, hoisting the `Android` checks, then adding ARM and MIPS support, then fixing any bugs).

Basically, all `version(Android)` checks need to be hoisted above `version(linux)` checks since GDC's `Android` implies `linux`. Also adding support for non-x86 platforms.

Maybe adding a `Linux` or `GNULinux` version would be better which is only defined if `linux && !Android`?