Install zstd in dist builder image.

Build libzstd from source because the EPEL package is built without fPIC.

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

@@ -62,6 +62,10 @@ COPY host-x86_64/dist-x86_64-linux/build-clang.sh /tmp/
 RUN ./build-clang.sh
 ENV CC=clang CXX=clang++
 
+# rustc's LLVM needs zstd.
+COPY scripts/zstd.sh /tmp/
+RUN ./zstd.sh
+
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 

src/ci/docker/scripts/zstd.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+set -ex
+
+hide_output() {
+  set +x
+  on_err="
+echo ERROR: An error was encountered with the build.
+cat /tmp/zstd_build.log
+exit 1
+"
+  trap "$on_err" ERR
+  bash -c "while true; do sleep 30; echo \$(date) - building ...; done" &
+  PING_LOOP_PID=$!
+  "$@" &> /tmp/zstd_build.log
+  trap - ERR
+  kill $PING_LOOP_PID
+  rm /tmp/zstd_build.log
+  set -x
+}
+
+ZSTD=1.5.6
+curl -L https://github.com/facebook/zstd/releases/download/v$ZSTD/zstd-$ZSTD.tar.gz | tar xzf -
+
+cd zstd-$ZSTD
+CFLAGS=-fPIC hide_output make -j$(nproc) VERBOSE=1
+hide_output make install
+
+cd ..
+rm -rf zstd-$ZSTD