Add log output when overriding a global option setting

[cresswellp]

If a <project>_ENABLE_<feature> variable is used, it's not directly referenced in the ecbuild.log output unless both that and ENABLE_<feature> are present (which triggers a warning). If only the project-specific variable is present and it differs from the default setting, the output can be confusing; for example, if we have ECCODES_ENABLE_NETCDF=OFF:

eccodes - DEBUG - ecbuild_add_option(NETCDF): defaults to ON
eccodes - DEBUG - ecbuild_evaluate_dynamic_condition(_NETCDF_condition): checking condition '' -> TRUE
eccodes - DEBUG - ecbuild_add_option(NETCDF): ENABLE_NETCDF not found in cache
eccodes - DEBUG - ecbuild_add_option(NETCDF): defining option ENABLE_NETCDF 'Support for GRIB to NetCDF conversion' ON
eccodes - DEBUG - ecbuild_add_option(NETCDF): ENABLE_NETCDF=ON
eccodes - DEBUG - ecbuild_add_option(NETCDF): feature disabled # !?!

In the last line the setting is suddenly disabled with no explanation.

The surrounding code has good logging coverage, so a few extra lines here would explain what's going on. This PR inserts a few extra lines of context:

...
eccodes - DEBUG - ecbuild_add_option(NETCDF): ENABLE_NETCDF=ON
eccodes - DEBUG - ecbuild_add_option(NETCDF): found ECCODES_ENABLE_NETCDF=OFF
eccodes - DEBUG - ecbuild_add_option(NETCDF): set ENABLE_NETCDF from ECCODES_ENABLE_NETCDF
eccodes - DEBUG - ecbuild_add_option(NETCDF): ENABLE_NETCDF=OFF
eccodes - DEBUG - ecbuild_add_option(NETCDF): feature disabled

Happy for this to be edited if you think it's now too verbose, but I think at least one extra line here would be useful.

[wdeconinck]

I am very happy with this extra verbose output in DEBUG logging. Thanks @cresswellp !