PR to put all root stuff into one script

[mcarans]

As per LW's suggestions, put all root stuff into one script.

Also adds Ubuntu latest test build

Only adds -std=gnu99 for gcc on Linux

[LW-archlinux]

19a9aa9 "We have to assume git installed otherwise another script needs root"

That will probably break build on archlinux as git is not in base-devel. You may be able to ensure git is present on arch github runners, but not on archlinux user systems.

[AnotherCommander]

Tested it on Windows with legacy and Clang environments, no issues,

Testing on Linux platforms will be required to confirm the Linux side of things, as I do not have such systems available for testing.

Lone Wolf's comment should also be considered, so I'll stand by for a bit before merging to give some time to act on that.

[mcarans]

@LW-archlinux I have updated the README to make it clear that the first step is to install git. I think it's reasonable for us to expect developers to do that since they need git to obtain the source code in the first place.

[mcarans]

@AnotherCommander I have added gameDirAddOnsPath to OOOXZManager.m to get the AddOns folder relative to AppImage if running an AppImage otherwise get ./Addons for Linux or ../AddOns for Windows as before.

[LW-archlinux]

@LW-archlinux I have updated the README to make it clear that the first step is to install git. I think it's reasonable for us to expect developers to do that since they need git to obtain the source code in the first place.

Agreed.