fontconfig: Program 'gperf' was overridden with the compiled executable 'gperf' and therefore cannot be used during configuration

`--wrap-mode=forcefallback` fails because `gperf` is not expected to be a wrap a this point. Unlike with dependency there is no `type_name()` to check if it is `internal`, so it fails.

Start by reproducing the `--wrap-mode=forcefallback` configuration failure described for the fontconfig wrap and trace how the `gperf` program is handled during configuration. Done means forcefallback no longer rejects or overrides `gperf` at this stage and the configuration completes successfully.

Written by the indexing model from the issue text.