Linux: engines and apps build in an Ubuntu 26.04 container, glibc 2.43 at most (L1.4)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/linux/container.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Usage: container.sh <command...>; runs it in Ubuntu 26.04.
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")/../.." && pwd)
+[ $# -gt 0 ] || {
+  echo "container.sh: give a command, such as scripts/build-libreoffice.sh" >&2
+  exit 1
+}
+image=ely-office-linux-build
+docker build -q -t "$image" "$root/packaging/linux" >/dev/null
+# Own target and Cargo home: host builds need newer glibc.
+mkdir -p "$root/target/ubuntu" "$root/target/ubuntu-cargo" "$root/target/ubuntu-home"
+docker run --rm --user "$(id -u):$(id -g)" -v "$root:$root" -w "$root" \
+  -e HOME="$root/target/ubuntu-home" -e CARGO_HOME="$root/target/ubuntu-cargo" \
+  -e CARGO_TARGET_DIR="$root/target/ubuntu" -e ELY_RELEASE_TOKEN \
+  "$image" "$@"