Allow break from a block called by mrb_yield; close #3359

This means #3701 is now OK to merge.

include/mruby/error.h

@@ -32,6 +32,13 @@ MRB_API mrb_noreturn void mrb_no_method_error(mrb_state *mrb, mrb_sym id, mrb_va
 /* declaration for fail method */
 MRB_API mrb_value mrb_f_raise(mrb_state*, mrb_value);
 
+struct RBreak {
+  MRB_OBJECT_HEADER;
+  struct iv_tbl *iv;
+  struct RProc *proc;
+  mrb_value val;
+};
+
 /**
  * Protect
  *

include/mruby/value.h

@@ -116,7 +116,8 @@ enum mrb_vtype {
   MRB_TT_DATA,        /*  21 */
   MRB_TT_FIBER,       /*  22 */
   MRB_TT_ISTRUCT,     /*  23 */
-  MRB_TT_MAXDEFINE    /*  24 */
+  MRB_TT_BREAK,       /*  24 */
+  MRB_TT_MAXDEFINE    /*  25 */
 };
 
 #include <mruby/object.h>