Boost 1.70.0 compile errors in VS2017 x86 /std:c++17 /clr

Hi,

I get compiler errors when trying to compile with 32 bit and CLR using Visual Studio 2017:

> libraries\boost\type_traits\detail\is_function_cxx_11.hpp(388): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(388): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(386): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(403): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(403): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(401): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(418): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(418): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(416): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(433): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(433): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(431): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(449): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(449): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(447): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(464): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(464): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(462): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(479): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(479): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(477): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(494): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(494): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(492): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(510): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(510): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(508): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(525): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(525): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(523): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(540): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(540): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(538): note: see declaration of 'boost::is_function'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(555): warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(555): error C2953: 'boost::is_function': class template has already been defined
libraries\boost\type_traits\detail\is_function_cxx_11.hpp(553): note: see declaration of 'boost::is_function'

Start with libraries\boost\type_traits\detail\is_function_cxx_11.hpp and reproduce the reported errors using Visual Studio 2017, x86, /std:c++17, and /clr. Trace the duplicate is_function definitions and calling-convention warnings; done means this configuration compiles without the reported errors.

Written by the indexing model from the issue text.