With new gpgrt-config and *.pc files, *-config can be replaced by gpgrt-config.
Since there are still old software which invokes *-config script in configure script (from *.m4), we should keep offering *-config scripts.
By improving gpg-error-config script (automatically detects the place for --libdir and also detects corresponding *.pc by its script name), gpg-error-config script can be the one which invokes gpgrt-config script with --libdir option and name for *.pc.
Then, all *-config script can be linked to gpg-error-config script.