CentOS7へGCC4.9.3をインストール ref: http://qiita.com/yn-misaki/items/601e260bec0b6eaaa74e

file0.txt

$ cat /etc/redhat-release
CentOS Linux release 7.2.1511 (Core)

file1.txt

$ yum list installed | grep gcc
$ sudo yum remove gcc libgcc

file2.txt

$ sudo yum install -y libmpc-devel mpfr-devel gmp-devel

file3.txt

$ cd /tmp
$ curl -O ftp://ftp.mirrorservice.org/sites/sourceware.org/pub/gcc/releases/gcc-4.9.3/gcc-4.9.3.tar.bz2
$ tar xvfj gcc-4.9.3.tar.bz2

file4.txt

$ cd gcc-4.9.3
$ make -j 4

file5.txt

$ sudo make install

file6.txt

$ gcc --version
gcc (GCC) 4.9.3
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.