wayland: Fix wayland session not starting on some systems

Fedora's mutter is built with --auto-features=enabled which enables
-initfd support. But the current meson code doesn't check whether
-initfd is available in Xwayland, leading to the wayland session not
starting up.

Check for -initfd's availability before enabling it.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1103

meson.build

@@ -396,11 +396,14 @@ if have_wayland
 
   # For Xwayland -initfd usage
   use_initfd = get_option('xwayland_initfd')
+  xwayland_options = run_command(xwayland_path, '-help')
   if use_initfd.auto()
-    xwayland_options = run_command(xwayland_path, '-help')
     have_xwayland_initfd = xwayland_options.stderr().contains('-initfd')
   else
     have_xwayland_initfd = use_initfd.enabled()
+    if have_xwayland_initfd and not xwayland_options.stderr().contains('-initfd')
+      error('XWayland -initfd support requested but not available')
+    endif
   endif
 
   if (have_xwayland_initfd)