Park CPPUnit linking in LDFLAGS instead of LIBS

The cppunit config program doesn't split them up, but it's more
convenient on Mac to put them in LDFLAGS, otherwise it tries to find
the Macports version of CPPUnit and it's annoying.

configure.ac

@@ -145,7 +145,7 @@ AS_IF([test "x$enable_cppunit" != "xno"], [
 
 if (test x$HAVE_CPPUNIT = x1); then
   antioch_optional_test_INCLUDES="$CPPUNIT_CPPFLAGS $antioch_optional_test_INCLUDES"
-  antioch_optional_test_LIBS="$CPPUNIT_LIBS $antioch_optional_test_LIBS"
+  antioch_optional_test_LDFLAGS="$CPPUNIT_LIBS $antioch_optional_test_LDFLAGS"
 fi
 AM_CONDITIONAL(ANTIOCH_ENABLE_CPPUNIT, test x$enablecppunit = xyes)