Take effect sysroot functionality to the default config file

When loading the default config file with FONTCONFIG_SYSROOT,
it fails if no /etc/fonts/fonts.conf is available, even if it is
there where is based on sysroot.

To address this, FcConfig is required to determine the sysroot.
therefore, this change makes FcConfigFilename() deprecated,
use FcConfigGetFilename() instead.

Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/181
4 files changed