Get wayland-session wrapper from environment.

diff --git a/daemon/gdm-session.c b/daemon/gdm-session.c
index 3b83fcd3..e60e6a57 100644
--- a/daemon/gdm-session.c
+++ b/daemon/gdm-session.c
@@ -2933,8 +2933,9 @@ gdm_session_start_session (GdmSession *self,
                                                            allow_remote_connections? "--allow-remote-connections " : "",
                                                            command);
                         } else {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s %s\"",
                                                            register_session ? "--register-session " : "",
+                                                           g_getenv ("GDM_WAYLAND_SESSION"),
                                                            command);
                         }
                 } else if (run_xsession_script) {
@@ -2965,8 +2966,9 @@ gdm_session_start_session (GdmSession *self,
                                                            register_session ? "--register-session " : "",
                                                            self->selected_program);
                         } else {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"dbus-run-session -- %s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"dbus-run-session -- %s %s\"",
                                                            register_session ? "--register-session " : "",
+                                                           g_getenv ("GDM_WAYLAND_SESSION"),
                                                            self->selected_program);
                         }
                 } else {
bmit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=a2c0dbb84a5537a0f9edb67dd20af3c7fe773aea'>root</a>/<a href='/guix/log/gnu?id=a2c0dbb84a5537a0f9edb67dd20af3c7fe773aea'>gnu</a>/<a href='/guix/log/gnu/services?id=a2c0dbb84a5537a0f9edb67dd20af3c7fe773aea'>services</a>/<a href='/guix/log/gnu/services/dict.scm?id=a2c0dbb84a5537a0f9edb67dd20af3c7fe773aea'>dict.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/dict.scm?id=a2c0dbb84a5537a0f9edb67dd20af3c7fe773aea&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-09-21 00:31:15 +0200'>2020-09-21</span></td><td><a href='/guix/commit/gnu/services/dict.scm?id=b864ddb6905a1c4e3a88a6e8214b58f42ff5bf19'>services: dicod: Reduce irony.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/dict.scm (dicod-service): Fix docstring typo.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-05-08 16:30:50 +0200'>2020-05-08</span></td><td><a href='/guix/commit/gnu/services/dict.scm?id=dd0804c67e99914eecc471fdb92f4220425a1cbc'>services: Add descriptions.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/dbus.scm (polkit-service-type)[description]: New field.
* gnu/services/dict.scm (dicod-service-type)[description]: New field.
* gnu/services/dns.scm (knot-service-type)[description]: New field.
* gnu/services/networking.scm (dhcpd-service-type)[description]: New field.
* gnu/services/shepherd.scm (shepherd-root-service-type)[description]:
New field.
* gnu/services/xorg.scm (slim-service-type)[description]: New field.
(screen-locker-service-type)[description]: New field.
* gnu/system/pam.scm (pam-root-service-type)[description]: New field.
* gnu/system/shadow.scm (account-service-type)[description]: New field.
</span></span></td><td>Ludovic Courtès</td></tr>