centos 7上编译gcc 4.9

1. 从github下载gcc 源码
   https://github.com/gcc-mirror/gcc/tree/releases/gcc-4.9.0
2. 安装必要的包
   yum install -y gmp-devel.x86_64 libmpc-devel.x86_64 mpfr-devel.x86_64 mpfr.x86_64 bison build-essential flex make automake gcc gcc-c++ kernel-devel glibc*.i686 libgcc*.i686 texi2html texinfo*
3. 解压缩gcc源码，cd到源码目录
4. 如有需要可以执行源码目录下contrib/download_prerequisites脚本下载必要的组件
5. mkdir build && cd build
6. …/configure --prefix=/opt/gcc-4.9/
7. make -j64
8. make install