Dependent ports use different c++ compilers

[mike at reifenberger.com]

Hi,
kicad-devel depends at least on two c++ libraries: boost-lib and 
webkit-gtk2.

kicad-devel and boost uses:
   USES+= compiler:c++11-lang
This leads at least under FreeBSD 9.3 and 10.* to the usage of clang++

webkit-gtk2 uses:
   USES += compiler:c++11-lib
This leads at least under FreeBSD 9.3 to the usage of GNU g++ (FreeBSD 
10+ is using clang++)
and this leads to missing symbols when linking kicad-devel.

How can this dilemma be resolved?

Greetings
---
Mike (mr@)