qemu-amd64: fix xfce4 background (!728)

[ci:skip-build]: already built successfully in CI

device/device-qemu-amd64/APKBUILD

@@ -1,6 +1,6 @@
 pkgname=device-qemu-amd64
 pkgver=1
-pkgrel=20
+pkgrel=21
 pkgdesc="Simulated device in qemu with an x86 platform"
 url="https://postmarketos.org"
 arch="x86_64"
@@ -11,6 +11,7 @@ makedepends=""
 subpackages="
 	$pkgname-x11
 	$pkgname-weston
+	$pkgname-xfce4
 	$pkgname-kernel-stable:kernel_stable
 	$pkgname-kernel-mainline:kernel_mainline
 "
@@ -37,6 +38,12 @@ weston() {
 		"$subpkgdir"/etc/xdg/weston/weston.ini
 }
 
+xfce4() {
+	install_if="$pkgname postmarketos-ui-xfce4"
+	install="$subpkgname.post-install"
+	mkdir "$subpkgdir"
+}
+
 kernel_stable() {
 	pkgdesc="Stable for everyday usage (recommended)"
 	depends="linux-postmarketos-stable"

device/device-qemu-amd64/device-qemu-amd64-xfce4.post-install

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+sed -i 's/monitor0/monitorVirtual-1/' /etc/skel/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml