use $libdir instead of $prefix/lib to find library dir

configure.in

@@ -46,7 +46,7 @@ AC_ARG_ENABLE(id3libtest, [  --disable-id3libtest       Do not try to compile an
 	elif test "x$id3lib_prefix" != "x" ; then
 		ID3LIB_LIBS="-L$id3lib_prefix/lib"
 	elif test "x$prefix" != "xNONE" ; then
-		ID3LIB_LIBS="-L$prefix/lib"
+		ID3LIB_LIBS="-L$libdir"
 	fi
 
 	ID3LIB_LIBS="$ID3LIB_LIBS -lid3"

src/libFLAC++/libFLAC++.m4

@@ -19,7 +19,7 @@ AC_ARG_ENABLE(libFLACPPtest, [  --disable-libFLACPPtest       Do not try to comp
   elif test "x$libFLACPP_prefix" != "x" ; then
     LIBFLACPP_LIBS="-L$libFLACPP_prefix/lib"
   elif test "x$prefix" != "xNONE" ; then
-    LIBFLACPP_LIBS="-L$prefix/lib"
+    LIBFLACPP_LIBS="-L$libdir"
   fi
 
   LIBFLACPP_LIBS="$LIBFLACPP_LIBS -lFLAC++ $LIBFLAC_LIBS"

src/libFLAC/libFLAC.m4

@@ -18,7 +18,7 @@ AC_ARG_ENABLE(libFLACtest, [  --disable-libFLACtest       Do not try to compile
   elif test "x$libFLAC_prefix" != "x" ; then
     LIBFLAC_LIBS="-L$libFLAC_prefix/lib"
   elif test "x$prefix" != "xNONE" ; then
-    LIBFLAC_LIBS="-L$prefix/lib"
+    LIBFLAC_LIBS="-L$libdir"
   fi
 
   LIBFLAC_LIBS="$LIBFLAC_LIBS -lFLAC -lm"

src/libOggFLAC++/libOggFLAC++.m4

@@ -19,7 +19,7 @@ AC_ARG_ENABLE(libOggFLACPPtest, [  --disable-libOggFLACPPtest       Do not try t
   elif test "x$libOggFLACPP_prefix" != "x" ; then
     LIBOGGFLACPP_LIBS="-L$libOggFLACPP_prefix/lib"
   elif test "x$prefix" != "xNONE" ; then
-    LIBOGGFLACPP_LIBS="-L$prefix/lib"
+    LIBOGGFLACPP_LIBS="-L$libdir"
   fi
 
   LIBOGGFLACPP_LIBS="$LIBOGGFLACPP_LIBS -lOggFLAC++ $LIBOGGFLAC_LIBS"

src/libOggFLAC/libOggFLAC.m4

@@ -18,7 +18,7 @@ AC_ARG_ENABLE(libOggFLACtest, [  --disable-libOggFLACtest       Do not try to co
   elif test "x$libOggFLAC_prefix" != "x" ; then
     LIBOGGFLAC_LIBS="-L$libOggFLAC_prefix/lib"
   elif test "x$prefix" != "xNONE" ; then
-    LIBOGGFLAC_LIBS="-L$prefix/lib"
+    LIBOGGFLAC_LIBS="-L$libdir"
   fi
 
   LIBOGGFLAC_LIBS="$LIBOGGFLAC_LIBS -lOggFLAC -lFLAC -lm"