Avoid invalid char to pointer conversion, fatal with clang 15.

Index: Makefile.PL
--- Makefile.PL.orig
+++ Makefile.PL
@@ -163,7 +163,7 @@ main ()
 #if defined (__stub_$f) || defined (__stub___$f)
 choke me
 #else
-f = $f ();
+f = $f;
 #endif
 
   ;