method.h: BITFIELD in rb_method_definition_t

* method.h (rb_method_definition_struct): use BITFIELD for
  rb_method_type_t.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62078 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

method.h

@@ -153,7 +153,7 @@ enum method_optimized_type {
 };
 
 PACKED_STRUCT_UNALIGNED(struct rb_method_definition_struct {
-    unsigned int type :  4; /* method type */
+    BITFIELD(rb_method_type_t) type : 4;
     int alias_count : 28;
     int complemented_count : 28;