Add dist:Gcc build step

To distribute the prebuilt libgccjit.so from CI.

Author: Kobzol

Diff for: src/bootstrap/src/core/build_steps/dist.rs

@@ -2464,3 +2464,30 @@ impl Step for ReproducibleArtifacts {
         if added_anything { Some(tarball.generate()) } else { None }
     }
 }
+
+/// Tarball containing a prebuilt version of the libgccjit library,
+/// needed as a dependency for the GCC codegen backend (similarly to the LLVM
+/// backend needing a prebuilt libLLVM).
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+pub struct Gcc {
+    pub target: TargetSelection,
+}
+
+impl Step for Gcc {
+    type Output = GeneratedTarball;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.alias("gcc")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(Gcc { target: run.target });
+    }
+
+    fn run(self, builder: &Builder<'_>) -> Self::Output {
+        let tarball = Tarball::new(builder, "gcc", &self.target.triple);
+        let output = builder.ensure(super::gcc::Gcc { target: self.target });
+        tarball.add_file(output.libgccjit, ".", 0o644);
+        tarball.generate()
+    }
+}

Diff for: src/bootstrap/src/core/builder/mod.rs

@@ -1072,6 +1072,7 @@ impl<'a> Builder<'a> {
                 dist::PlainSourceTarball,
                 dist::BuildManifest,
                 dist::ReproducibleArtifacts,
+                dist::Gcc
             ),
             Kind::Install => describe!(
                 install::Docs,

Diff for: 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()]);
         }