ci: add runners for vanilla LLVM 14 and 15

.github/workflows/ci.yml

@@ -291,6 +291,14 @@ jobs:
           - name: x86_64-gnu-distcheck
             os: ubuntu-20.04-xl
             env: {}
+          - name: x86_64-gnu-llvm-15
+            env:
+              RUST_BACKTRACE: 1
+            os: ubuntu-20.04-xl
+          - name: x86_64-gnu-llvm-14
+            env:
+              RUST_BACKTRACE: 1
+            os: ubuntu-20.04-xl
           - name: x86_64-gnu-llvm-13
             env:
               RUST_BACKTRACE: 1

src/ci/docker/host-x86_64/x86_64-gnu-llvm-14/Dockerfile

@@ -0,0 +1,67 @@
+FROM ubuntu:22.04
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+# NOTE: intentionally installs both python2 and python3 so we can test support for both.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  g++ \
+  gcc-multilib \
+  make \
+  ninja-build \
+  file \
+  curl \
+  ca-certificates \
+  python2.7 \
+  python3 \
+  git \
+  cmake \
+  sudo \
+  gdb \
+  llvm-14-tools \
+  llvm-14-dev \
+  libedit-dev \
+  libssl-dev \
+  pkg-config \
+  zlib1g-dev \
+  xz-utils \
+  nodejs \
+  && rm -rf /var/lib/apt/lists/*
+
+# Install powershell (universal package) so we can test x.ps1 on Linux
+RUN curl -sL "https://github.com/PowerShell/PowerShell/releases/download/v7.3.1/powershell_7.3.1-1.deb_amd64.deb" > powershell.deb && \
+    dpkg -i powershell.deb && \
+    rm -f powershell.deb
+
+COPY scripts/sccache.sh /scripts/
+RUN sh /scripts/sccache.sh
+
+# We are disabling CI LLVM since this builder is intentionally using a host
+# LLVM, rather than the typical src/llvm-project LLVM.
+ENV NO_DOWNLOAD_CI_LLVM 1
+
+# Using llvm-link-shared due to libffi issues -- see #34486
+ENV RUST_CONFIGURE_ARGS \
+      --build=x86_64-unknown-linux-gnu \
+      --llvm-root=/usr/lib/llvm-14 \
+      --enable-llvm-link-shared \
+      --set rust.thin-lto-import-instr-limit=10
+
+# NOTE: intentionally uses all of `x.py`, `x`, and `x.ps1` to make sure they all work on Linux.
+ENV SCRIPT ../x.py --stage 2 test --exclude src/tools/tidy && \
+           # Run the `mir-opt` tests again but this time for a 32-bit target.
+           # This enforces that tests using `// EMIT_MIR_FOR_EACH_BIT_WIDTH` have
+           # both 32-bit and 64-bit outputs updated by the PR author, before
+           # the PR is approved and tested for merging.
+           # It will also detect tests lacking `// EMIT_MIR_FOR_EACH_BIT_WIDTH`,
+           # despite having different output on 32-bit vs 64-bit targets.
+           ../x --stage 2 test tests/mir-opt \
+                             --host='' --target=i686-unknown-linux-gnu && \
+           # Run the UI test suite again, but in `--pass=check` mode
+           #
+           # This is intended to make sure that both `--pass=check` continues to
+           # work.
+           #
+           ../x.ps1 --stage 2 test tests/ui --pass=check \
+                             --host='' --target=i686-unknown-linux-gnu && \
+           # Run tidy at the very end, after all the other tests.
+           python2.7 ../x.py --stage 2 test src/tools/tidy

src/ci/docker/host-x86_64/x86_64-gnu-llvm-15/Dockerfile

@@ -0,0 +1,67 @@
+FROM ubuntu:22.10
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+# NOTE: intentionally installs both python2 and python3 so we can test support for both.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  g++ \
+  gcc-multilib \
+  make \
+  ninja-build \
+  file \
+  curl \
+  ca-certificates \
+  python2.7 \
+  python3 \
+  git \
+  cmake \
+  sudo \
+  gdb \
+  llvm-15-tools \
+  llvm-15-dev \
+  libedit-dev \
+  libssl-dev \