Install GCC 4.9.4

install-gcc-4.9.4.sh

#!/bin/bash

# this script installs GCC 4.9.4 
# to use it navigate to your home directory and type:
# sh install-gcc-4.9.4.sh

# download and install gcc 4.9.4
wget https://ftp.gnu.org/gnu/gcc/gcc-4.9.4/gcc-4.9.4.tar.gz
tar xzf gcc-4.9.4.tar.gz
cd gcc-4.9.4
./contrib/download_prerequisites
cd ..
mkdir objdir

cd objdir
../gcc-4.9.4/configure --prefix=$HOME/gcc-4.9.4 --enable-languages=c,c++,fortran,go --disable-multilib
make

# install
make install

# clean up
rm -rf ~/objdir
rm -f ~/gcc-4.9.4.tar.gz

# add to path (you may want to add these lines to $HOME/.bash_profile)
export PATH=$HOME/gcc-4.9.4/bin:$PATH
export LD_LIBRARY_PATH=$HOME/gcc-4.9.4/lib:$HOME/gcc-4.9.4/lib64:$LD_LIBRARY_PATH

FAIL.
new gcc can't properly compile old gcc. and 4.9.x binaries have conflicts with libmpfr*