My Linux station is based on Ubuntu 14.10 -- yeah I know this is pretty old --. All graphical tools (Mesa, LLVM, RadeonSI) and the Linux kernel are maintained and I try to keep theom up-to-date. However I would like to upgrade my gcc version.

I am currently testing information shared at https://gist.github.com/application2000/73fd6f4bf1be6600a2cf9f56315a2d91

Ok let see if it works
apt-get update && sudo apt-get install build-essential software-properties-common -y
add-apt-repository ppa:ubuntu-toolchain-r/test -y
apt-get update
apt-get install gcc-snapshot -y 
apt-get update
Now it failed with this
root@amdgaming:~# apt-get install gcc-6 g++-6 -y 
Lecture des listes de paquets... Fait
Construction de l'arbre des dépendances       
Lecture des informations d'état... Fait
E: Impossible de trouver le paquet gcc-6
E: Impossible de trouver le paquet g++-6
E: Impossible de trouver de paquet correspondant à l'expression rationnelle « g++-6 »
After googling on "install gcc-6 ubuntu" let's try this one http://juniway.blogspot.fr/2015/06/install-gcc510-on-ubuntu-1204build-from.html
apt-get install libgmp-dev libmpfr-dev libmpc-dev libc6-dev
Time to download sources
cd /opt/Sources
wget https://ftp.gnu.org/gnu/gcc/gcc-6.2.0/gcc-6.2.0.tar.bz2
Try configure, build and install
./configure --prefix=/opt/gcc-6.2.0 --disable-checking --enable-languages=c,c++,objc --disable-multilib --with-system-zlib
make -j4
make install

Notice: for commands above I took decision to install it in /opt/gcc-6.2.0. I don't want to break compiler gcc-4.9 suite installed on my own system. This way gcc-4.9 is kept safe on my system

Check installed version

root@amdgaming:/opt/Sources/gcc-6.2.0# /opt/gcc-6.2.0/bin/gcc -v
Utilisation des specs internes.
COLLECT_GCC=/opt/gcc-6.2.0/bin/gcc
COLLECT_LTO_WRAPPER=/opt/gcc-6.2.0/libexec/gcc/i686-pc-linux-gnu/6.2.0/lto-wrapper
Cible : i686-pc-linux-gnu
Configuré avec: ./configure --prefix=/opt/gcc-6.2.0 --disable-checking --enable-languages=c,c++,objc --disable-multilib --with-system-zlib
Modèle de thread: posix
gcc version 6.2.0 (GCC) 
root@amdgaming:/opt/Sources/gcc-6.2.0# /opt/gcc-6.2.0/bin/gcc --version
gcc (GCC) 6.2.0
Copyright © 2016 Free Software Foundation, Inc.
Ce logiciel est libre; voir les sources pour les conditions de copie.  Il n'y a PAS
GARANTIE; ni implicite pour le MARCHANDAGE ou pour un BUT PARTICULIER.