version: use git to get short commit SHA and date (!7) · Merge requests · CHS / Cmake Fortran Scripts · GitLab

Update of the version cmake script to use git for specific information:

if a development version was specified, add the short commit SHA
```
1.0.0-dev0 -> 1.0.0-dev0+02d7e12
```
if no version_date.txt file is present, or we again have a development version, we will use the commit date instead of the current date

If git was not found, or the files were copied outside to repo, the current behavior will be used.