puppet: Build wal-g from source for aarch64.

Since wal-g does not provide binaries for aarch64, build them from
source.  While building them from source for arm64 would better ensure
that build process is tested, the build process takes 7min and 700M of
temp files, which is an unacceptable cost; we thus only build on
aarch64.

Since the wal-g build process uses submodules, which are not in the
Github export, we clone the full wal-g repository.  Because the
repository is relatively small, we clone it anew on each new version,
rather than attempt to manage the remotes.

Fixes #21070.

scripts/lib/build-wal-g

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+
+set -eux
+
+apt-get install -y \
+    liblzo2-dev \
+    libbrotli-dev \
+    libsodium-dev \
+    build-essential \
+    gcc \
+    cmake \
+    libc-dev
+
+tmpdir="$(mktemp -d)"
+trap 'rm -r "$tmpdir"' EXIT
+
+export GOCACHE="$tmpdir/cache"
+export GOPATH="$tmpdir/build"
+
+src_dir="/srv/zulip-wal-g-src-$1"
+dst="/srv/zulip-wal-g-$1"
+
+cd "$src_dir"
+
+if [ "$(git rev-parse HEAD)" != "$2" ]; then
+    echo "Commit tag has changed; expected $2, got $(git rev-parse HEAD)"
+    exit 1
+fi
+
+export PATH="$PATH:$GOBIN"
+export USE_LZO=1
+export USE_LIBSODIUM=1
+make deps pg_build
+
+mv "main/pg/wal-g" "$dst"