Top level local variable is not file scope with mruby command

[shuujii]

Is the following behavior intentional?

Files

# a.rb
a = 1

# b.rb
p a

mruby

$ bin/mruby -r ./a.rb b.rb
1

Ruby

$ ruby -r ./a.rb b.rb
Traceback (most recent call last):
b.rb:1:in `<main>': undefined local variable or method `a' for main:Object (NameError)

[dearblue]

I tried to fix it as #4933, but @shuujii pointed out a new problem.
#4933 (comment)

Based on that, I discovered and commented on a problem that occurred in mruby binary and will leave it here too.
#4933 (comment)
#4933 (comment)

# c.rb
a, b, c = 1, 2, 3
A = -> { b = -2; [a, b, c] }

# d.rb
a, b = 5, 6
p A.call
p a, b

% bin/mrbc c.rb
% bin/mrbc d.rb
% bin/mruby -b -r c.rb d.rb
[5, -2, main]
5
-2

This result can also be confirmed at https://travis-ci.com/dearblue/mruby/jobs/281490648#L1473.