Initial ARM64 build support
Updates PKGBUILDs to include aarch64, and updates the builder Dockerfile to create an AMD64 and ARM64 base image, and conditionals uses one based on TARGETARCH (Docker built-in arg).
Updates PKGBUILDs to include aarch64, and updates the builder Dockerfile to create an AMD64 and ARM64 base image, and conditionals uses one based on TARGETARCH (Docker built-in arg).