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.
Note that rust_bin does not include rls in this version, as the current
incarnation depends on an unsupported dependency. Rls seems to be
falling out of favour for rust-analyser anyway, so this is not a
blocker.