win32/perlhost.h: revert changes to SETUPEXCHANGE

This was broken by 48bda52, which removed the `*` before `xptr`.
Without `*`, we set our `iptr` (a class member) to a bogus pointer, and
the assignment to `xptr` (which is a function parameter and hence a
local variable) is effectively dead code.

Author: mauke

win32/perlhost.h

@@ -2143,11 +2143,11 @@ CPerlHost::CPerlHost(void)
 #define SETUPEXCHANGE(xptr, iptr, table) \
     STMT_START {				\
         if (xptr) {				\
-            *(void**)&iptr = (void*)xptr;			\
-            *(void**)&xptr = (void*)&table;			\
+            iptr = *xptr;			\
+            *xptr = &table;			\
         }					\
         else {					\
-            *(void**)&iptr = (void*)&table;			\
+            iptr = &table;			\
         }					\
     } STMT_END