libfyaml now mandatory

@k203161 reported that since v3.9.1 libfyaml became mandatory, even if configured with --disable-mci.

This is due to the yac_compute_weights tool.

The desired behaviour from O-YAC is, that without MCI the requirements should be minimal. I would support that! Whether this includes workout MCI but with tools could be discussed.

If there is something like HAVE_FYAML, we could handle it like NetCDF. Everything can be build but if you call it, an error will be raised if it was configured without it.

@k202160 or @k202215 can you take care of that and generate a new release once this has been solved?