fetch and build TCC from github repository

[JoGei]

Addresses issue #108

TODO:

• Decide which commit of TCC should be used, Tested with latest commit to their main branch mop
• Fix CI Test steps?
• Decide whether we want to make "fetch+build TCC" work for Windows host. won't fix thanks for not asking.

[JoGei]

Got to make the build work again for Ubuntu-latest, aka 22. In case of Unix, TCC is now fetched from maintained repos, while Windows still uses the old one. If we want to make it work for Windows, some form of MinGW would be necessary as explained in TCC sources.

Biggest problem with our current flow is, IMHO, that the RegisterJITfile macro requires existing files during CMake configuration. Because of this I had to run the build steps for TCC during configuration as execute_process instead of having them be part of the usual CMake build process. This feels a bit hacky, but works.

This PR fails CI, because of "Linux Test" which requires Boost libraries to be present of which I am not sure how they could be if "Requirements" are not run before the test jobs. As far as I understand the CI, only the packaged etiss working directory is transferred from build to test(?).