It’s probably not installed as the default os is something like 2-3 years old (Ubuntu 14.04). Thankfully there is an APT repo set up that contains newer version of the GCC software.
sudo apt-get update
sudo apt install gcc-6
After a few minutes you should be able to type:
emarcotte:~/workspace $ gcc-6 --version
gcc-6 (Ubuntu/Linaro 6.3.0-18ubuntu2~14.04) 6.3.0 20170519
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