gdm: use official Xsession

Fixes loading the profile on X11 sessions.

srcpkgs/gdm/files/Xsession

@@ -1,2 +0,0 @@
-#!/bin/sh
-exec $@

srcpkgs/gdm/template

@@ -1,7 +1,7 @@
 # Template file for 'gdm'
 pkgname=gdm
 version=42.0
-revision=2
+revision=3
 build_helper="gir"
 build_style=meson
 configure_args="
@@ -9,7 +9,7 @@ configure_args="
  -Dtcp-wrappers=false -Dscreenshot-dir=/var/lib/gdm/greeter
  -Dplymouth=enabled -Dxauth-dir=/run/gdm -Dpid-file=/run/gdm/gdm.pid
  -Dsystemd-journal=false -Dinitial-vt=7 -Dwayland-support=true
- -Dselinux=disabled -Dlibaudit=disabled
+ -Dselinux=disabled -Dlibaudit=disabled -Dgdm-xsession=true
  -Dsystemdsystemunitdir=/usr/lib/systemd/system
  -Dsystemduserunitdir=/usr/lib/systemd/user"
 hostmakedepends="dconf gettext itstool pkg-config"
@@ -49,8 +49,6 @@ if [ "$CROSS_BUILD" ]; then
 fi
 
 post_install() {
-	vinstall $FILESDIR/Xsession 755 etc/gdm
-
 	for f in $DESTDIR/etc/pam.d/*; do
 		if grep -q "pam_systemd.so" "$f"; then
 			vsed -i "s/pam_systemd\.so/pam_elogind.so/" "$f"