working gcc update procedure

[DavidJRichards]

I used the procedure here to update gcc from v9 to v11 with the option to select either using update-alternatives and also installed the gui galternatives to help configure and select the default compiler.

https://tutorialforlinux.com/2021/05/23/step-by-step-gcc-11-1-linux-mint-20-installation/

The demos build and run using Qemu in Linux Mint 20.3, I have not yet tried using a floppy on a real PC.

[jeanthom]

Thanks for reporting back, I'll include this in the README.