我想用最新版本的gcc.
Ubuntu 14.04 带有 gcc 4.8.2，但是有 4.9.0 可用，而且，我看到它可以作为一个包使用：gcc-4.9. 我尝试安装它
sudo apt-get install gcc-4.9
但它说
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'gcc-4.9-base' for regex 'gcc-4.9'
gcc-4.9-base is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
看起来它已经安装了，只是不是默认的？我如何利用它来构建我的程序？