[Fontconfig] performance regression: fc-cache became slow when skipping

[Patrick Lam]

Mike FABIAN wrote:
> I.e. the second run of fc-cache in the ~/.fonts directory not even
> twice as fast as the first run.

I've committed a patch which uses directory cache files in fc-cache, if
-f was not specified, like 2.3.2 did.  I think this fixes your issue.

pat