temporarily enable PERL_RC_STACK for CI smoking

lets see what breaks

Author: iabyn

perl.h

@@ -25,7 +25,7 @@
 /* Treat the SVs on the argument stack as having been reference counted.
  * (Experimental).
  */
-/* #define PERL_RC_STACK */
+#define PERL_RC_STACK /* XXX tmp */
 
 #ifdef PERL_MICRO
 #   include "uconfig.h"