d95efef896
The arm path hardcoded ARCH=x86_64 and the x86_64 type2 runtime, so a `build_release.sh arm` run produced a broken AppImage (x86_64 runtime wrapping an aarch64 binary). Derive ARCH and the runtime file from the target arch, and have toolchain.sh fetch runtime-aarch64 alongside runtime-x86_64. This restores GRIM's linux-arm AppImage release type; verified the output is an ARM aarch64 AppImage.