Since we require meson 1.3(.2), we can modernize the usage a bit,
as well as improve some logic
- use / instead of join_paths
- use option.allowed() instead of !option.disable()
- use cxx.get_supported_arguments
- use fs.copyfile instead of configure_file
- show a summary at the end of the configuration
When meson is run in a build path that is different from source root, the
generated shared library cannot be found under "<source_root>/guile". This
patch adds the corresponding path under build root to guile_root_path so that
they continue to work.
This should fix https://github.com/djcb/mu/issues/2631.
