After some fiddling with GitHub actions I managed to add DJGPP compilation support.
It can now use DJGPP - GCC 12.2.0 and DJGPP - GCC 4.8.5. To get GCC 4.8.5 to work I had to include stdint.h and remove some older specific redeclarations of uint*.
Running tests is really hard to do AFAIK when cross-compiling like this, so it only checks if it can run make all. Maybe when I've updated Adplay for DOS I could look into some way of adding tests there. (Also see adplug/adplay-dos#3)

Build results are available in my fork: https://github.com/AranVink/adplug/actions/runs/6091183567

Please review and let me know what you think. I'm very sorry for the commit spam, I thought I was only pushing to my own repository while doing these tests, but unfortunately this PR and CI still got triggered through my own repo/branch. 😅

I am quite busy the next two weeks, but I will try to grab some time every now and and probably rebuild to commit history (doing some git rebase magic)

Much appreciated, if you want me to make a new PR with all commits squashed let me know (I made this mess 😉)

I rebased your tree, so unless you are very familier with git, just do a fresh clone of your own git repository on your computer.

I believe a lot of the fiddling with setting CXXFLAGS etc. to include -I/foo/djgpp/include can be avoided if djgpp extracted into /usr/local/djgpp, as that is probably the PREFIX is was compiled for.

I think some fixes from here could be already pushed to master, like header and type fixes. They are trivial.

Thank you for revisiting this. I'll take another look this weekend on the CXXFLAGS/paths.

Are there any other concerns or attention points that would prevent this from being merged in the near future? I'd like this PR to be as complete as possible, so I can continue with upgrading Adplay for DOS.

We are getting close to something now (git rebase is needed again to clean up the history)

Sorry for the extra spam lately, trying to make the github workflow be a smooth as possible.

Thank you for your patience

Thank you for following up and making the tweaks so it can be merged, again much appreciated. I'll continue working on Adplay for DOS, building a CD pipeline, and maybe even a CI pipeline (when tooling allows).