Fix enumeration mutation function prototype to match what clang expects (id instead of void* argument).

mutation.m

@@ -1,9 +1,10 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include "objc/runtime.h"
 
 // This function is exported as a weak symbol to enable GNUstep or some other
 // framework to replace it trivially
-void __attribute__((weak)) objc_enumerationMutation(void *obj)
+void __attribute__((weak)) objc_enumerationMutation(id obj)
 {
 	fprintf(stderr, "Mutation occured during enumeration.");
 	abort();