nixos/xserver,gdm: let GDM handle X server verbosity.

nixos/modules/services/x11/display-managers/gdm.nix

@@ -102,6 +102,7 @@ in
     # GDM needs different xserverArgs, presumable because using wayland by default.
     services.xserver.tty = null;
     services.xserver.display = null;
+    services.xserver.verbose = null;
 
     services.xserver.displayManager.job =
       {

nixos/modules/services/x11/xserver.nix

@@ -480,6 +480,15 @@ in
         '';
       };
 
+      verbose = mkOption {
+        type = types.nullOr types.int;
+        default = 3;
+        example = 7;
+        description = ''
+          Controls verbosity of X logging.
+        '';
+      };
+
       useGlamor = mkOption {
         type = types.bool;
         default = false;
@@ -631,10 +640,11 @@ in
       [ "-config ${configFile}"
         "-xkbdir" "${cfg.xkbDir}"
         # Log at the default verbosity level to stderr rather than /var/log/X.*.log.
-        "-verbose" "3" "-logfile" "/dev/null"
+         "-logfile" "/dev/null"
       ] ++ optional (cfg.display != null) ":${toString cfg.display}"
         ++ optional (cfg.tty     != null) "vt${toString cfg.tty}"
         ++ optional (cfg.dpi     != null) "-dpi ${toString cfg.dpi}"
+        ++ optional (cfg.verbose != null) "-verbose ${toString cfg.verbose}"
         ++ optional (!cfg.enableTCP) "-nolisten tcp"
         ++ optional (cfg.autoRepeatDelay != null) "-ardelay ${toString cfg.autoRepeatDelay}"
         ++ optional (cfg.autoRepeatInterval != null) "-arinterval ${toString cfg.autoRepeatInterval}"