[boost] improve <boost/config.hpp>

Hi, for more compatibility with existing boost-macros/defines I came up with - see attachment. 1) Is that correct in principle? 2) Problem: for BOOST_NO_CXX23_HDR_XXX I use __has_include. However, __has_include is not guaranteed to exist. How about the solution? 3) Did I miss useful things? thx Gero