It looks like Travis isn't configured correctly for Linux clang.

We do not want to be checking for MSVC in particular. Instead what we want is to be using the config macro BOOST_NO_CXX11_ALLOCATOR to determine what the code should be. So please remove all the:

#if !((__cplusplus > 201700) || (defined(_MSVC_LANG) && (_MSVC_LANG > 201700)))

and substitute in its place:

#if defined(BOOST_NO_CXX11_ALLOCATOR)

then test.

I updated .travis.yml. g++ 7 in C++17 mode fails one test though, due to a compiler bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81311. I reported that 5 months ago but nothing seems to have happened on that front, so perhaps we need to #ifdef that out for g++ 7 in C++17 mode?

Yes, we do need to #ifdef it out, and we did, in eba4893. :-)

@eldiener

and substitute in its place:
#if defined(BOOST_NO_CXX11_ALLOCATOR)

Great - done. That was my preferred solution in the first place. But then I chose to follow Boost.Config's precedent on this particular topic ...

Thanks for implementing this change.