Use environment to trigger Qt5 builds
Ports Qt5 commit: Make sure QIconLoader is always initialized

Port of Qt5 commit aa5f70c00a88edcddd26e8fea767a40e8c5c31b8

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Get and set XDG user dirs variables in config file

Config file set in $XDG_CONFIG_HOME/user-dirs.dirs.