Like with ccache, we want to make sure the git checkout is considered
clean during build.

Placing these directories at the root will make the git revision
detection consider the working directory to be dirty.

Fixes: KartKrew/Kart#1405

The "clone" strategy clones the entire repository, which takes
a significant amount of time. It's not needed, because the default
"fetch" strategy will reuse the executor's local clone and clean it
before the job scripts run.

There's no need to let these artifacts pile up since the only ones that
will be relevant to non-programmers are the latest from any given ref.

Ring Racers' object file output is considerably larger than SRB2.
50M is insufficient to hold even a single build.

The singular .gitlab-ci.yml is pretty beefy. Splitting it into
smaller files by job and job template will make maintaining the
individual jobs easier.

Fix backwards compat for SPR2 Super (resolves #1225)

Closes #1225

See merge request STJr/SRB2!2410

Fix buffer overflow when invoking MusicChange hook

See merge request STJr/SRB2!2441

Fix SOC freeslotting including trailing spaces in constant names

See merge request STJr/SRB2!2415

Sprite names up to 64 character long and 256 frames per sprite

See merge request STJr/SRB2!2394

replace CPM with vcpkg

See merge request STJr/SRB2!2321

Make Extra Time powerup work in old-style special stages

See merge request STJr/SRB2!2292

Support LF_MIXNIGHTSCOUNTDOWN for old-style special stages

See merge request STJr/SRB2!2291

Fix softlock on old special stages when running out of time due to being hit

See merge request STJr/SRB2!2398