wget http://ftp.tsukuba.wide.ad.jp/software/gcc/infrastructure/gmp-6.1.0.tar.bz2
tar xvf gmp-6.1.0.tar.bz2
cd gmp-6.1.0/
./configure --prefix=/home/myaccount/
make
make check（しないと、怒られる）
make install

wget http://ftp.tsukuba.wide.ad.jp/software/gcc/infrastructure/mpfr-3.1.4.tar.bz2
tar xvf mpfr-3.1.4.tar.bz2
cd mpfr-3.1.4/
./configure --prefix=/home/myaccount/ --with-gmp=/home/myaccount/
make
make install

wget http://ftp.tsukuba.wide.ad.jp/software/gcc/infrastructure/mpc-1.0.3.tar.gz
tar xvf mpc-1.0.3.tar.gz
cd mpc-1.0.3/
./configure --prefix=/home/myaccount/ --with-mpfr=/home/myaccount/
make
make install

wget http://ftp.tsukuba.wide.ad.jp/software/gcc/releases/gcc-4.9.4/gcc-4.9.4.tar.bz2
tar xvf gcc-4.9.4.tar.bz2
cd gcc-4.9.4/
export LD_LIBRARY_PATH=/home/myaccount/lib; ./configure --prefix=/home/myaccount/ -with-gmp=/home/myaccount/ --with-mpfr=/home/myaccount/ --with-mpc=/home/myaccount/ --disable-multilib
make
make install

$gcc --version
gcc (GCC) 4.9.4
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.

**************************************************************************************************************************************************************************
configure-stage1-target-libgcc
というエラーが出るので、
export LD_LIBRARY_PATH=/home/myaccount/lib
する。

.bash_profile に追記した。

lib64 を忘れていたので、修正。
export LD_LIBRARY_PATH=/home/myaccount/lib64:/home/myaccount/lib
**************************************************************************************************************************************************************************

gmp　The GNU Multiple Precision Arithmetic Library　多倍長演算ライブラリ
mpfr　C library for multiple-precision floating-point computations　多倍長浮動小数点演算ライブラリ
mpc　C library for the arithmetic of complex numbers　複素数演算ライブラリ