fix for -fno-common
https://gitweb.gentoo.org/repo/gentoo.git/commit/media-sound/scmpc/files?id=c9f42ac8feb314f3f2f6ec7cfd8c535ff33fe735

Index: src/mpd.h
--- src/mpd.h.orig
+++ src/mpd.h
@@ -32,7 +32,7 @@
 /**
  * MPD connection data
  */
-struct {
+struct mpd_t {
 	struct mpd_connection *conn;
 	struct mpd_status *status;
 	struct mpd_song *song;
@@ -42,7 +42,9 @@ struct {
 	guint idle_source;
 	guint check_source;
 	guint reconnect_source;
-} mpd;
+};
+
+extern struct mpd_t mpd;
 
 /**
  * Connect to MPD