try to make freebsd clang build move along a bit

configure.in

@@ -178,7 +178,7 @@ elif test "x${ax_cv_c_compiler_vendor}" = "xclang" ; then
             SOLINK="-dynamic -force-flat-namespace"
         ;;
         *)
-            AC_ERROR([Please update configure.in with SOLINK values for your compiler])
+            SOLINK="-shared -Xlinker -x"
         ;;
 
     esac