centos7 更新 gcc
参考链接：
https://stackoverflow.com/questions/36327805/how-to-install-gcc-5-3-with-yum-on-centos-7-2
yum install centos-release-scl yum install devtoolset-7-gcc* scl enable devtoolset-7 bash which gcc gcc --version
参考链接：
https://stackoverflow.com/questions/36327805/how-to-install-gcc-5-3-with-yum-on-centos-7-2
yum install centos-release-scl yum install devtoolset-7-gcc* scl enable devtoolset-7 bash which gcc gcc --version
