Added linux support

[scandown]

I've changed some of the code on the linux side so that there isn't anymore errors. This includes multiple redefinitions which has now been resolved.

[ColleagueRiley]

That change should be pushed out to PureDoom. That specific line is outdated code from the original 1997 Linux doom.

[scandown]

Are you recommending I commit those two commits to the main PureDOOM repository?

[scandown]

Also the second commit made does fix a problem found in this project. As when you include the alsa audio header, it redefines the timespec and timeval structs so adding "#define _POSIX_C_SOURCE" prevents that from happening.

[ColleagueRiley]

Just the one in PureDoom is necessary, PureDoom is not my project and if it has an issue it should be fixed upstream as well.

[scandown]

Just the one in PureDoom is necessary, PureDoom is not my project and if it has an issue it should be fixed upstream as well.

I've made a pull request for the PureDoom project so thats all good.

However I'd recommend the other commit to be pushed into this project for the reason said before.

[ColleagueRiley]

There's still an error because of

#include <alsa/asoundlib.h>

That can be safely removed I added it while trying to add MIDI support, which didn't seem to work correctly. So you can remove the Alsa code in this PR so that way it compiles on linux if you'd like.

Otherwise adding libasound2-dev to the apt install command in the CI .yml for linux would also prevent this issue.

[scandown]

I've now added that library to the workflow and it seems to be all good, do you reckon its now good for merging?

[ColleagueRiley]

looks good, thanks