GitLab

Switch kernel builds away from using xargo

See merge request !1255

Use cargo's 'build-std=core,alloc' instead.

Also: Cargo is now given the complete path to the target specific JSON file.
This forces the use of the JSON file (the file is silently ignored if
the target in question was built into the rust compiler).

Update .gitlab-ci.yml

See merge request !1248

Allow logging serial from qemu to a file.

See merge request !1247

Setting the qemu_serial_logfile variable in your .config to a file path
will cause the serial output from qemu to be mirrored to that file.
Signed-off-by: Wren Turkal <wt@penguintechs.org>