use packaged libxmp instead of bundled libxmp-lite, works around
build issue when libxmp package is installed

Index: source/audiolib/src/multivoc.cpp
--- source/audiolib/src/multivoc.cpp.orig
+++ source/audiolib/src/multivoc.cpp
@@ -45,7 +45,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Bos
 
 #ifdef HAVE_XMP
 # define BUILDING_STATIC
-# include "libxmp-lite/xmp.h"
+# include <xmp.h>
 
 int MV_XMPInterpolation = XMP_INTERP_NEAREST;
 #endif