[spotify] Add missing include of config.h

src/inputs/spotify_librespotc.c

@@ -14,6 +14,10 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>