Index: configure.ac
===================================================================
--- configure.ac	(revision 147098)
+++ configure.ac	(working copy)
@@ -1344,7 +1344,7 @@
 AC_ARG_WITH(ppl_lib, [  --with-ppl-lib=PATH     Specify the directory for the installed PPL library])
 
 case $with_ppl in 
-  no)
+  no|"")
     ppllibs=
     ;;
   *)
@@ -1399,7 +1399,7 @@
 AC_ARG_WITH(cloog_lib, [  --with-cloog-lib=PATH   Specify the directory for the installed CLooG library])
 
 case $with_cloog in 
-  no)
+  no|"")
     clooglibs=
     clooginc=
     ;;