Add git version info to usage output.

[RaymiiOrg]

I'm not sure how you feel about including a version number, here's a quick demo with cmake and git, included in the
main output (if no args are given). It might be suitable until actual versions/releases are managed.

Here's example output:

[21:35:59] [remy@gateway] [ ~/tmp/axpbox/build (git_version_info_in_usage_output) ]
$ ./axpbox 
AXPBox Alpha Emulator
Git version info: SHA1: 6ef090e610f2a154e11b645c8f72a3dbeb3fe3bd; Date: Sat Nov 7 21:34:46 2020; Commit subject: Add git version info to usage output. Includes commit hash, commit date and commit subject.
Usage: ./axpbox run|configure <options>

No substitute for an actual version number, but does give users information about which build they're running. Now that so many improvements are happening, it will probably help with bug reports in the future, if it's known which version is being used.

[lenticularis39]

This is certainly a good idea considering more and more people are discovering AXPbox, therefore using it and stumbling upon various bugs.

The version message is too long in my opinion, I suppose something like this would suffice:

AXPBox Alpha Emulator (commit d1b81289593412bfe4b61c87e550451ec2693f0b)
Usage: ./axpbox run|configure <options>

One can always look up the commit message and so on in the commit history if needed.

About the implementation: the GITINFO variable could be included in config.h.in among the PACKAGE_ variables (which are currently unused if I'm correct - they were carried over from es40). I believe there is no need to have other variables inside the config header and this one directly on the command line.

[RaymiiOrg]

The version message is too long in my opinion, I suppose something like this would suffice:

AXPBox Alpha Emulator (commit d1b81289593412bfe4b61c87e550451ec2693f0b)
Usage: ./axpbox run|configure <options>

Changed it to be just the hash.

About the implementation: the GITINFO variable could be included in config.h.in among the PACKAGE_ variables (which are currently unused if I'm correct - they were carried over from es40). I believe there is no need to have other variables inside the config header and this one directly on the command line.

Was not aware of what a cmakedefine does, but that is nicer indeed. Updated the code to use them.

[lenticularis39]

Nice, thanks for the changes :)