Bind can't use `boost::result_of`

I discovered that `boost::bind` strongly requires to have `result_type` meta-field from the type of the passed functional object. I was surprised, because why not to use `boost::result_of` when possible?
Can we fix it, even it will be a breaking change?

The shortest-reproducible example here:
https://godbolt.org/z/5fhb1hdYa