Auto merge of #122658 - cuviper:gccjit-archive, r=Mark-Simulacrum

ci: Build gccjit from a git archive

A full `git clone` of GCC includes quite a lot of history, and it's
completely unnecessary for building it in CI. We can use a GitHub
archive URL to get a simple tarball that is much faster to download.

Also, the `gcc-build` directory can be removed after install to reduce
the image size even further.

Author: bors