Any reasonably new version of fontconfig does search that path by default,
and setting this globally causes problems, as 2.10 and 2.11 need
incompatible configs.
Tested: slim+xfce desktop, chrootenv-ed steam.
I have no idea why we were setting the global variable;
e.g., neither Fedora nor Ubuntu does that.
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
