Building and installing with cargo now works again.
During installation it ignores the Cargo.lock of redox_install crate
and uses version 0.2.12 which would break the code without this fix.

Update toolchain to 2022-03-18

See merge request !8

Signed-off-by: Tim Crawford <tcrawford@system76.com>

Get TARGET from the environment

See merge request redox-os/redoxer!6

Checks against a static list of targets. This makes it possible to use
redoxer with AArch64 as well as x86_64.

Update ubuntu version (for glibc 2.29 required by cargo)

See merge request redox-os/redoxer!4

- redoxer install will call cargo install
- redoxer toolchain will install toolchain