[gtk/gtk-3-24] gdk quartz: add missing include (-Werror=implicit)

[John Ralls <jralls src gnome org>]

commit 5e8d97ef0b375883d4f265a78c272197f27c51e3
Author: Thomas Holder <thomas thomas-holder de>
Date:   Sun Feb 2 11:16:40 2020 +0100

    gdk quartz: add missing include (-Werror=implicit)
    
    Regression of GNOME/gtk!641 (ef72fe750adc)

 gdk/quartz/gdkglcontext-quartz.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gdk/quartz/gdkglcontext-quartz.c b/gdk/quartz/gdkglcontext-quartz.c
index f259eef8e3..5c4b8e7ac9 100644
--- a/gdk/quartz/gdkglcontext-quartz.c
+++ b/gdk/quartz/gdkglcontext-quartz.c
@@ -28,6 +28,7 @@
 #include "gdkquartzglcontext.h"
 #include "gdkquartzwindow.h"
 #include "gdkprivate-quartz.h"
+#include "gdkquartz-gtk-only.h"
 
 #include "gdkinternals.h"