hints/solaris_2.sh of checking to see if uselongdouble is defined is a good
idea.
+=item Call status
+
+Call-backs are only called always, even if the value for the call-back is
+uset: UU/usethreads.cbu is called when Configure is about to deal with
+threads. All created call-backs from hints should thus check the status
+of the variable, and act upon it.
+
=item Future status
I hope this "call-back" scheme is simple enough to use but powerful