bug#32773: [PATCH] Fix clang libstdc++ header location search

[Mathieu Othacehe]

> Applying both your patch and my patch works for me, in both pure and
> non-pure environments. I would suggest taht we also hide clang in the
> same way as gcc is hidden (in favour of clang-toolchain) to avoid
> confusion, but otherwise it seems these two patches together at least
> get things to a working state!

Great! 

> I'd like to see make-clang-toolchain allow you to pick between a
> specific libstdc++ or libc++, but that requires more thinking so I
> think ideally it'd be better to apply these patches first to get things
> to a fixed state.

I agree. Let's wait to see if someone has objections and I'll push both
patches in a few days.

Thanks for your support on this :)

Mathieu