Rollup merge of #137667 - Kobzol:gcc-dist-build, r=onur-ozkan

Add `dist::Gcc` build step

This PR adds a `dist:Gcc` bootstrap step to distribute a prebuilt `libgccjit.so` from CI on x64 Linux.

With primed sccache, the build takes ~4 minutes on CI, and produces a 50 MiB archive.

I want to land this before adding something akin to `[gcc] download-ci-gcc = true`, to already have the artifacts available on CI, to make it easier to setup the download merge-base logic.

r? ``@ghost``

src/tools/opt-dist/src/main.rs

@@ -389,6 +389,7 @@ fn main() -> anyhow::Result<()> {
             "clippy",
             "miri",
             "rustfmt",
+            "gcc",
         ] {
             build_args.extend(["--skip".to_string(), target.to_string()]);
         }