Revert "no need to install g++-6 alongside clang"
Revert "no need to install g++-6 alongside clang"

This reverts commit 6b0092e57bb24275f182341336cb10074accaba1.

accosmin/nanocv,accosmin/nanocv,accosmin/nano,accosmin/nanocv,accosmin/nano,accosmin/nano