boost assumes libc++ is only used by clang

[RJVB (René Bertin)]

While testing the idea of using libc++ while building C++ code with G++ I ran into (amost) exactly the errors shown here : ​http://stackoverflow.com/questions/41050942/clang-modules-interaction-with-std-iterator-and-boost-move-iterator-hpp/43983903

In this case the errors were not caused by libc++ but by the simple fact that in a few locations, boost assumes that libc++ is only used with clang.

After fixing those presumptions with the attached patch I was able to build both boost and digiKam5 (which uses Boost and is a good test for any C++ compiler).

[neverpanic (Clemens Lang)]

I think this should go to boost upstream.

[RJVB (René Bertin)]

it probably should, but in that case we should probably first update the port

[ryandesign (Ryan Carsten Schmidt)]

No, it should be reported to the developers of boost first (if it's still a problem). They are more familiar with their code than we are and are better able to judge what changes are appropriate. If they agree and fix it and release a new version then we can update to that version or we can cherry-pick their commit into a patch until a new version is released.