Add docs and test for BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS

The pull request addresses comments to the commit https://github.com/boostorg/config/commit/411399ec60c0f56e77aa56da830945100a4b263e.

- The macro is now defined when defaulted functions are not supported at all.
- Docs and test added.
- The macro is no longer defined for gcc 4.4 as it passes the test.