[gtk/gtk-3-24-meson] meson: gtk docs: set ENABLE_ON_X11

[Christoph Reiter <creiter src gnome org>]

commit 6145fe0e4d00228c53359d2c6a7d7fd8a575145e
Author: Christoph Reiter <creiter src gnome org>
Date:   Sun Mar 31 19:06:56 2019 +0200

    meson: gtk docs: set ENABLE_ON_X11

 docs/reference/gtk/meson.build | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/docs/reference/gtk/meson.build b/docs/reference/gtk/meson.build
index f97c545d10..3e8c50d971 100644
--- a/docs/reference/gtk/meson.build
+++ b/docs/reference/gtk/meson.build
@@ -452,6 +452,12 @@ else
   types_conf.set('DISABLE_ON_QUARTZ', '')
 endif
 
+if x11_enabled
+  types_conf.set('ENABLE_ON_X11', '')
+else
+  types_conf.set('ENABLE_ON_X11', '%')
+endif
+
 if get_option('documentation')
 
     configure_file(input: 'version.xml.in', output: 'version.xml', configuration: version_conf)