Auto merge of rust-lang#107651 - Kobzol:ci-single-cgu, r=<try>

[WIP] Build `rustc` with a single CGU on x64 Linux

Follow-up attempt to rust-lang#87650. I wonder if anything changed with the addition of LTO.

I also enabled a single CGU only for the actual build of the compiler on CI, so that we can better see the perf. effects on the bootstrap benchmark.

.github/workflows/ci.yml

@@ -529,7 +529,6 @@ jobs:
   try:
     name: "try - ${{ matrix.name }}"
     env:
-      DIST_TRY_BUILD: 1
       CI_JOB_NAME: "${{ matrix.name }}"
       CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
       HEAD_SHA: "${{ github.event.pull_request.head.sha || github.sha }}"

src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile

@@ -84,7 +84,8 @@ ENV RUST_CONFIGURE_ARGS \
       --set llvm.ninja=false \
       --set rust.jemalloc \
       --set rust.use-lld=true \
-      --set rust.lto=thin
+      --set rust.lto=thin \
+      --set rust.codegen-units=1
 
 ENV SCRIPT python3 ../x.py build --set rust.debug=true opt-dist && \
     ./build/$HOSTS/stage0-tools-bin/opt-dist python3 ../x.py dist \

src/ci/github-actions/ci.yml

@@ -689,7 +689,7 @@ jobs:
     <<: *base-ci-job
     name: try - ${{ matrix.name }}
     env:
-      DIST_TRY_BUILD: 1
+#      DIST_TRY_BUILD: 1
       <<: [*shared-ci-variables, *prod-variables]
     if: github.event_name == 'push' && (github.ref == 'refs/heads/try' || github.ref == 'refs/heads/try-perf') && github.repository == 'rust-lang-ci/rust'
     strategy: