x86_64 is used as a baseline: the "x86_64" entry, whatever status it has,
is transformed into "all", and then the other entries in ARCHITECTURES
either dropped or rearranged appropriately.
Add the cargo command to the package. Rust's package management tool is now
included in the package. The rationale for inclusion versus external package
is that the cargo command is closely related to the version of the rustc
compiler, and with the future dependency of the rust build system on cargo
they are closely linked.
The recipe is based on the official github sources, plus patches where
applicable. The tree including patches can be found at
https://github.com/nielx/rust
waddlesplash