[rhythmbox] Declared rb_metadata_iface_xml with extern

[Jonathan Matthew <jmatthew src gnome org>]

commit 6bf5a52b7047e3af8c731fc09e9210e723600ed7
Author: Andrew Brown <andrew andrewdbrown com>
Date:   Sun Mar 1 19:10:13 2015 -0500

    Declared rb_metadata_iface_xml with extern
    
    Because `rb-metadata-dbus.h` is included in multiple places
    `rb_metadata_iface_xml` needs to be declared with `extern` in order for
    Rhythmbox to build on Mac OS X with GCC 4.2.1.  (Apple's variant of GCC
    may be more strict in this manner.)
    
    It's probably best if it's declared with `extern` anyway since there
    should only be one definition.

 metadata/rb-metadata-dbus.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/metadata/rb-metadata-dbus.h b/metadata/rb-metadata-dbus.h
index 46d0d39..93f82f3 100644
--- a/metadata/rb-metadata-dbus.h
+++ b/metadata/rb-metadata-dbus.h
@@ -46,7 +46,7 @@ G_BEGIN_DECLS
 #define RB_METADATA_DBUS_TIMEOUT       (15000)
 #define RB_METADATA_SAVE_DBUS_TIMEOUT  (120000)
 
-const char *rb_metadata_iface_xml;
+extern const char *rb_metadata_iface_xml;
 
 GVariantBuilder *rb_metadata_dbus_get_variant_builder (RBMetaData *md);