Build process generated numerous locale warnings like:
bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
perl: warning: Setting locale failed
This happened because the Docker container and host environment were
configured to use `en_US.UTF-8`, but the rootfs cache may not contain
this locale (only `C.utf8` and whatever `DEST_LANG` specifies,
e.g. `en_GB.utf8`).
When `chroot_sdcard` runs commands inside the rootfs, environment variables
are inherited from the host/Docker, causing locale lookup failures.
Then use `C.UTF-8` locale for the build environment instead of `en_US.UTF-8`.
This locale is always available in rootfs immediately after mmdebstrap,
requiring no generation.
Changes
`lib/functions/host/docker.sh`: Remove `en_US.UTF-8` locale generation,
set `LANG=C.UTF-8` in container environment
`lib/functions/host/prepare-host.sh`: Change locale exports
from `en_US.UTF-8` to `C.UTF-8`
3e71438048