Refactor vm_defined to return a boolean

We just need this function to return whether or not the thing we're
looking for is defined.  If it's defined, return something true,
otherwise false.

insns.def

@@ -667,12 +667,10 @@ defined
 (VALUE val)
 // attr bool leaf = leafness_of_defined(op_type);
 {
+    val = Qnil;
     if (vm_defined(ec, GET_CFP(), op_type, obj, v)) {
       val = needstr;
     }
-    else {
-      val = Qnil;
-    }
 }
 
 /* check `target' matches `pattern'.

vm_insnhelper.c

@@ -3969,7 +3969,7 @@ vm_once_clear(VALUE data)
 
 /* defined insn */
 
-static enum defined_type
+static VALUE
 check_respond_to_missing(VALUE obj, VALUE v)
 {
     VALUE args[2];
@@ -3978,10 +3978,10 @@ check_respond_to_missing(VALUE obj, VALUE v)
     args[0] = obj; args[1] = Qfalse;
     r = rb_check_funcall(v, idRespond_to_missing, 2, args);
     if (r != Qundef && RTEST(r)) {
-	return DEFINED_METHOD;
+	return Qtrue;
     }
     else {
-	return DEFINED_NOT_DEFINED;
+	return Qfalse;
     }
 }
 
@@ -3989,42 +3989,31 @@ static VALUE
 vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_type, VALUE obj, VALUE v)
 {
     VALUE klass;
-    enum defined_type expr_type = DEFINED_NOT_DEFINED;
     enum defined_type type = (enum defined_type)op_type;
 
     switch (type) {
       case DEFINED_IVAR:
-	if (rb_ivar_defined(GET_SELF(), SYM2ID(obj))) {
+        return rb_ivar_defined(GET_SELF(), SYM2ID(obj));
-	    expr_type = DEFINED_IVAR;
-	}
 	break;
       case DEFINED_GVAR:
-	if (rb_gvar_defined(SYM2ID(obj))) {
+        return rb_gvar_defined(SYM2ID(obj));
-	    expr_type = DEFINED_GVAR;
-	}
 	break;
       case DEFINED_CVAR: {
         const rb_cref_t *cref = vm_get_cref(GET_EP());
         klass = vm_get_cvar_base(cref, GET_CFP(), 0);
-	if (rb_cvar_defined(klass, SYM2ID(obj))) {
+        return rb_cvar_defined(klass, SYM2ID(obj));
-	    expr_type = DEFINED_CVAR;
-	}
 	break;
       }
       case DEFINED_CONST:
       case DEFINED_CONST_FROM: {
 	bool allow_nil = type == DEFINED_CONST;
 	klass = v;
-        if (vm_get_ev_const(ec, klass, SYM2ID(obj), allow_nil, true)) {
+        return vm_get_ev_const(ec, klass, SYM2ID(obj), allow_nil, true);
-	    expr_type = DEFINED_CONST;
-	}
 	break;
       }
       case DEFINED_FUNC:
 	klass = CLASS_OF(v);
-	if (rb_ec_obj_respond_to(ec, v, SYM2ID(obj), TRUE)) {
+        return rb_ec_obj_respond_to(ec, v, SYM2ID(obj), TRUE);
-	    expr_type = DEFINED_METHOD;
-	}
 	break;
       case DEFINED_METHOD:{
 	VALUE klass = CLASS_OF(v);
@@ -4039,20 +4028,20 @@ vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_
 		    break;
 		}
 	      case METHOD_VISI_PUBLIC:
-		expr_type = DEFINED_METHOD;
+                return Qtrue;
 		break;
 	      default:
 		rb_bug("vm_defined: unreachable: %u", (unsigned int)METHOD_ENTRY_VISI(me));
 	    }
 	}
 	else {
-	    expr_type = check_respond_to_missing(obj, v);
+	    return check_respond_to_missing(obj, v);
 	}
 	break;
       }
       case DEFINED_YIELD:
 	if (GET_BLOCK_HANDLER() != VM_BLOCK_HANDLER_NONE) {
-	    expr_type = DEFINED_YIELD;
+            return Qtrue;
 	}
 	break;
       case DEFINED_ZSUPER:
@@ -4063,16 +4052,12 @@ vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_
 		VALUE klass = vm_search_normal_superclass(me->defined_class);
 		ID id = me->def->original_id;
 
-		if (rb_method_boundp(klass, id, 0)) {
+		return rb_method_boundp(klass, id, 0);
-		    expr_type = DEFINED_ZSUPER;
-		}
 	    }
 	}
 	break;
       case DEFINED_REF:{
-	if (vm_getspecial(ec, GET_LEP(), Qfalse, FIX2INT(obj)) != Qnil) {
+	return vm_getspecial(ec, GET_LEP(), Qfalse, FIX2INT(obj)) != Qnil;
-	    expr_type = DEFINED_GVAR;
-	}
 	break;
       }
       default:
@@ -4080,12 +4065,7 @@ vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_
 	break;
     }
 
-    if (expr_type != 0) {
-        return Qtrue;
-    }
-    else {
     return Qfalse;
-    }
 }
 
 static const VALUE *