Run check-mode UI tests in CI against big endian target

This validates that 64bit.be.stderr files are up to date; we don't run
32 bit big endian in CI as of this commit.

Author: Mark-Simulacrum

.github/workflows/ci.yml

@@ -262,6 +262,9 @@ jobs:
           - name: test-various
             os: ubuntu-20.04-xl
             env: {}
+          - name: test-big-endian
+            os: ubuntu-20.04-xl
+            env: {}
           - name: wasm32
             os: ubuntu-20.04-xl
             env: {}

src/ci/docker/host-x86_64/test-big-endian/Dockerfile

@@ -0,0 +1,30 @@
+FROM ubuntu:20.04
+
+COPY scripts/cross-apt-packages.sh /scripts/
+RUN sh /scripts/cross-apt-packages.sh
+
+COPY scripts/crosstool-ng-1.24.sh /scripts/
+RUN sh /scripts/crosstool-ng-1.24.sh
+
+COPY scripts/rustbuild-setup.sh /scripts/
+RUN sh /scripts/rustbuild-setup.sh
+USER rustbuild
+WORKDIR /tmp
+
+COPY host-x86_64/dist-powerpc64-linux/shared.sh host-x86_64/dist-powerpc64-linux/powerpc64-linux-gnu.config host-x86_64/dist-powerpc64-linux/build-powerpc64-toolchain.sh /tmp/
+RUN ./build-powerpc64-toolchain.sh
+
+USER root
+
+COPY scripts/sccache.sh /scripts/
+RUN sh /scripts/sccache.sh
+
+ENV PATH=$PATH:/x-tools/powerpc64-unknown-linux-gnu/bin
+
+ENV \
+    AR_powerpc64_unknown_linux_gnu=powerpc64-unknown-linux-gnu-ar \
+    CC_powerpc64_unknown_linux_gnu=powerpc64-unknown-linux-gnu-gcc \
+    CXX_powerpc64_unknown_linux_gnu=powerpc64-unknown-linux-gnu-g++
+
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV SCRIPT python3 ../x.py test --target powerpc64-unknown-linux-gnu src/test/ui --pass check --test-args --run=never

src/ci/docker/host-x86_64/test-big-endian/build-powerpc64-toolchain.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -ex
+
+source shared.sh
+
+mkdir build
+cd build
+cp ../powerpc64-linux-gnu.config .config
+hide_output ct-ng build
+cd ..
+rm -rf build