ci: add a runner for vanilla LLVM 19

src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile

@@ -0,0 +1,62 @@
+FROM ubuntu:24.10
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  g++ \
+  gcc-multilib \
+  make \
+  ninja-build \
+  file \
+  curl \
+  ca-certificates \
+  python3 \
+  git \
+  cmake \
+  sudo \
+  gdb \
+  llvm-19-tools \
+  llvm-19-dev \
+  libedit-dev \
+  libssl-dev \
+  pkg-config \
+  zlib1g-dev \
+  xz-utils \
+  nodejs \
+  mingw-w64 \
+  # libgccjit dependencies
+  flex \
+  libmpfr-dev \
+  libgmp-dev \
+  libmpc3 \
+  libmpc-dev \
+  && rm -rf /var/lib/apt/lists/*
+
+# Install powershell (universal package) so we can test x.ps1 on Linux
+# FIXME: need a "universal" version that supports libicu74, but for now it still works to ignore that dep.
+RUN curl -sL "https://github.com/PowerShell/PowerShell/releases/download/v7.3.1/powershell_7.3.1-1.deb_amd64.deb" > powershell.deb && \
+    dpkg --ignore-depends=libicu72 -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
+ENV EXTERNAL_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-19 \
+      --enable-llvm-link-shared \
+      --set rust.thin-lto-import-instr-limit=10
+
+COPY host-x86_64/dist-x86_64-linux/shared.sh /scripts/
+COPY host-x86_64/dist-x86_64-linux/build-gccjit.sh /scripts/
+
+RUN /scripts/build-gccjit.sh /scripts
+
+COPY scripts/x86_64-gnu-llvm.sh /tmp/script.sh
+ENV SCRIPT /tmp/script.sh

src/ci/github-actions/jobs.yml

@@ -247,6 +247,11 @@ auto:
   - image: x86_64-gnu-distcheck
     <<: *job-linux-8c
 
+  - image: x86_64-gnu-llvm-19
+    env:
+      RUST_BACKTRACE: 1
+    <<: *job-linux-8c
+
   - image: x86_64-gnu-llvm-18
     env:
       RUST_BACKTRACE: 1