Add GitLab CI with Linux builds on Alpine, Arch, Fedora, and Ubuntu using
both make and meson build systems.
Generated-by: Claude Code 1.0.65 (claude-sonnet-4@20250514)
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>