The method name becomes `call` in backtrace inside a block outside a method

#### mruby

```console
$ bin/mruby -e '1.times{raise}'
trace (most recent call last):
	[2] -e:1
	[1] mrblib/numeric.rb:77:in times
-e:1:in call: RuntimeError
```

#### Ruby

```console
$ ruby -e '1.times{raise}'
Traceback (most recent call last):
	2: from -e:1:in `<main>'
	1: from -e:1:in `times'
-e:1:in `block in <main>': unhandled exception
```