block_given? always returns false when it calls in block

[suzukaze]

Fix #2695
I made sure #2665, #2678 are not destroyed.

block_given? always returns false when it calls in block.
block cannot recieve block.

Could you tell me a sample code that block_given? return true in block.

[cremno]

Could you tell me a sample code that block_given? return true in block.

Something like this? (It doesn't return true anymore after applying your patch.)

def foo; define_singleton_method(:bar) { block_given? }; end; foo {}; bar

[suzukaze]

@cremno Thank you very much.
I close this PR.