use File::HomeDir;
use File::Which;

my $config;

# 1
if ( which( 'xdg-user-dir' ) ) {
    $config = File::HomeDir::FreeDesktop->my_config();
}
else {
    $config = File::HomeDir->my_data();
}

# 2
if ( $^O eq 'Unix' ) {
    $config = File::HomeDir::FreeDesktop->my_config();
}
else {
    $config = File::HomeDir->my_data();
}