Consider to add loong64 support

loong64 might become popular, particular in China. So supporting it would be welcome in principle, even though I currently have no hardware to test it with.

@msojocs, I am hesitant to build anything that I cannot test. Would a "Loongson 2K1000LA" development board be good to test this?

Testing using qemu could be a potential fallback.

References
* https://github.com/AppImage/type2-runtime/pull/109
* https://en.wikipedia.org/wiki/Loongson
* https://github.com/AppImage/type2-runtime/pull/33
* https://github.com/AppImage/appimagetool/pull/53