Drop dependency on Boost.Static_Assert

[akrzemi1]

Currently Boost.Optional still depends on Boost.Static_Assert and uses BOOST_STATIC_ASSERT instead of static_asseet.

This is due to an omission in the process. I depprecated (three releases ago) the support for certain C++11 workarounds (see the list), but I forgot about the static_assert. So while we now can use the listed C++11 features, it is still unsafe to use static_assert.

Ultimately, we want to be able to use static_assert in Boost.Optional. This requires two steps.

1. Determine if there even exist compilers that support rvalue references, variadic templates, fuction ref-qualifiers, but do not support static_assert. consult the maintainers of Boost.Config. If there aren't such compilers, just drop the dependency on Boost.Static_Assert right away.
2. Start the three-release depprecation period for BOOST_NO_CXX11_STATIC_ASSERT.

[typenametea]

What would be the best way to consult the maintainers, should I put a message out on the mailing list?

[akrzemi1]

That would be one way. Or just ask on Slack.