Bug#1100871: fontconfig-config: postinst fails and breaks installation in minimal build chroots without /usr/local/share/

[Luca Boccassi]

Package: fontconfig-config
Version: 2.15.0-2.1
Severity: serious
Justification: package uninstallable on minimal chroots

Dear Maintainer(s),

The NMU for #962420 moved a 'mkdir' in fontconfig-config.postinst out
of an 'if' statement, so now when it fails the postinst aborts and the
package installation fails.
This happens on minimal build systems, like the Open Build Service,
when the package is pulled in as a build dependency, as
/usr/local/share/ is not present on the builder. The fix is trivial,
the mkdir needs to use '-p' so that it creates the parent directories
if missing too.

I have uploaded an NMU to DELAYED/1 given it's already in testing.