Staleness of fontconfig 2.11.1 causing problems

[wlottoculus]

fontconfig 2.11.1 is confused by config files from newer versions of fontconfig, causing it to spew lots of warnings like:

Fontconfig warning: line 5: unknown element "its:rules"
Fontconfig warning: line 6: unknown element "its:translateRule"
Fontconfig error: line 6: invalid attribute 'translate'
Fontconfig error: line 6: invalid attribute 'selector'
Fontconfig error: line 7: invalid attribute 'xmlns:its'
Fontconfig error: line 7: invalid attribute 'version'
Fontconfig warning: line 9: unknown element "description"
Fontconfig warning: "/etc/fonts/conf.d/10-hinting-slight.conf", line 4: unknown element "its:rules"
Fontconfig warning: "/etc/fonts/conf.d/10-hinting-slight.conf", line 5: unknown element "its:translateRule"
Fontconfig error: "/etc/fonts/conf.d/10-hinting-slight.conf", line 5: invalid attribute 'translate'
Fontconfig error: "/etc/fonts/conf.d/10-hinting-slight.conf", line 5: invalid attribute 'selector'
Fontconfig error: "/etc/fonts/conf.d/10-hinting-slight.conf", line 6: invalid attribute 'xmlns:its'
Fontconfig error: "/etc/fonts/conf.d/10-hinting-slight.conf", line 6: invalid attribute 'version'
Fontconfig warning: "/etc/fonts/conf.d/10-hinting-slight.conf", line 8: unknown element "description"

and to take excessive time to initialize. A test program consisting of nothing but:

use fontconfig::fontconfig as ffi;

fn main() {
    unsafe {
        let d = ffi::FcInitLoadConfigAndFonts();
        ffi::FcConfigDestroy(d);
    }
}

takes more than 10 seconds on my machine running Fedora. Replacing the embedded fontconfig sources with version 2.13.92 causes the warnings to disappear and drop the runtime of said program to less than a tenth of a second.

I only hit this because I did not have the fontconfig-devel package installed. Installing that package causes build.rs to use my system fontconfig instead of using the embedded font config.