[gtk/popup-shadow-width] Add compatibility shim for g_memdup2()

[Matthias Clasen <matthiasc src gnome org>]

commit f0a44ba02bedb7bcea2cae3f9ffd1546f802f1a5
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Feb 4 19:27:22 2021 +0000

    Add compatibility shim for g_memdup2()
    
    We don't necessarily want to depend on a newer version of GLib, given
    that we're not really using g_memdup() in the wrong way.

 gdk/gdk-private.h | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/gdk/gdk-private.h b/gdk/gdk-private.h
index 3df7d3215c..fb3c18cd6f 100644
--- a/gdk/gdk-private.h
+++ b/gdk/gdk-private.h
@@ -49,4 +49,12 @@ guint gdk_parse_debug_var (const char        *variable,
                            const GdkDebugKey *keys,
                            guint              nkeys);
 
+/* Backward compatibility shim, to avoid bumping up the minimum
+ * required version of GLib; most of our uses of g_memdup() are
+ * safe, and those that aren't have been fixed
+ */
+#if !GLIB_CHECK_VERSION (2, 67, 3)
+# define g_memdup2(mem,size)    g_memdup((mem),(size))
+#endif
+
 #endif /* __GDK__PRIVATE_H__ */