[DO NOT MERGE] ci: what if we try to reclaim some space in between?

Author: jieyouxu

src/ci/docker/host-x86_64/x86_64-gnu-debug/Dockerfile

@@ -50,6 +50,11 @@ ENV RUST_CONFIGURE_ARGS \
 # - That the tests with `//@ needs-force-clang-based-tests` pass, since they
 #   don't run by default unless RUSTBUILD_FORCE_CLANG_BASED_TESTS is set.
 
+# HACK(jieyouxu): this first does a gigantic stage 2 full build with full debug
+# info, then cleans stage 2 artifacts to reclaim some disk space to make it
+# possible to run the stage 2 run-make test suite without running out of disk
+# space.
 ENV SCRIPT \
   python3 ../x.py --stage 2 build && \
+  python3 ../x.py --stage 2 clean && \
   python3 ../x.py --stage 2 test tests/run-make