Bug 1661450 - Move GTK2 checks behind MOZ_X11 r=stransky

GTK2 isn't compatible with Wayland and requires X11. No functional
change.

Differential Revision: https://phabricator.services.mozilla.com/D88797

old-configure.in

@@ -1588,14 +1588,13 @@ if test "$COMPILE_ENVIRONMENT"; then
     AC_DEFINE_UNQUOTED(GDK_VERSION_MAX_ALLOWED,$GDK_VERSION_MAX_ALLOWED)
   fi
   if test "$MOZ_ENABLE_GTK"; then
-    if test "$MOZ_X11"; then
-      GDK_PACKAGES=gdk-x11-2.0
-    fi
     AC_DEFINE_UNQUOTED(GLIB_VERSION_MIN_REQUIRED,$GLIB_VERSION_MIN_REQUIRED)
     AC_DEFINE_UNQUOTED(GLIB_VERSION_MAX_ALLOWED,$GLIB_VERSION_MAX_ALLOWED)
 
-    PKG_CHECK_MODULES(MOZ_GTK2, gtk+-2.0 >= $GTK2_VERSION gtk+-unix-print-2.0 glib-2.0 >= $GLIB_VERSION gobject-2.0 gio-unix-2.0 $GDK_PACKAGES)
-    MOZ_GTK2_CFLAGS="-I${_topsrcdir}/widget/gtk/compat $MOZ_GTK2_CFLAGS"
+    if test "$MOZ_X11"; then
+      PKG_CHECK_MODULES(MOZ_GTK2, gtk+-2.0 >= $GTK2_VERSION gtk+-unix-print-2.0 glib-2.0 >= $GLIB_VERSION gobject-2.0 gio-unix-2.0 gdk-x11-2.0)
+      MOZ_GTK2_CFLAGS="-I${_topsrcdir}/widget/gtk/compat $MOZ_GTK2_CFLAGS"
+    fi
   fi
 fi # COMPILE_ENVIRONMENT