[boost] [release][proto]: MSVC 19.24.28314 (VS 2019 16.4.0) )won't compile proto's generate.hpp

Hi, the latest MSVC version (shipped with VS 2019 16.4.0) doesn't compile boost/proto/generate.hpp since there is an old MSVC-fix, which is no longer needed, and now even produces errors. The "develop" branch of proto contains a fix for that since 2015 (!) but it never made it to the master branch. (https://github.com/boostorg/proto/issues/20) Could some please merge it over to make it into release 1.72 - would be really great! Tobias