Here's a patch for guile-readline/Makefile.am that creates the link to 
readline.scm in a portable way. In addition to the patch, the macro 
AC_PROG_LN_S has to be added to guile-readline/configure.in.

There's a section called "When Automake Isn't Enough->Extending 
Automake Rules" in the Automake manual that shows how to create links 
portably.