Deprecate C-API

[tmadlener]

BEGINRELEASENOTES

• Deprecate the C-API which is used by the fortran interface. However, since no one seems to be actively using that interface we introduce a deprecation warning for the C-API to see if that has any users outside of the internal fortran interface. If you are seeing deprecation messages in your build outputs please let us know.
• Fix F77 tests and run them in the CI.
  • Degrade some compiler errors back to warnings for gcc10 as it has become more strict than previous versions.

ENDRELEASENOTES

The SimTrackerHitImpl::setCellID function does not exist in cpp, so it probably shouldn't exist for the fortran API either. Also added the non-deprecated lcsthgetcellid0 and lcsthgetcellid1 to the API (implementations were already present).

[tmadlener]

Seems like gcc10 is a bit more stringent than previous versions:

• https://github.com/iLCSoft/LCIO/runs/2519286870?check_suite_focus=true#step:4:485
• https://github.com/iLCSoft/LCIO/runs/2519286851?check_suite_focus=true#step:4:563
• https://github.com/iLCSoft/LCIO/runs/2519286851?check_suite_focus=true#step:4:587

Also there seem to be some additional warnings that are all similar to this one here: https://github.com/iLCSoft/LCIO/runs/2519286851?check_suite_focus=true#step:4:407

However, my limited fortran knowledge is not enough to have an idea of how to fix these.

[andresailer]

Isn't Whizard using the C API?

[tmadlener]

From what we gathered, both Whizard and SGV implement/generate their own Fortran API for LCIO which does not use the C API.

[andresailer]

Ok, thanks for the information!