Use gcc 4.9.4 in CI

[gibfahn]

Now that nodejs/node#13466 has landed, we need to make sure all our boxes have the newer compiler levels.

According to @bnoordhuis in nodejs/node#13466 (comment), binaries built with the later version should run everywhere they did before, so there shouldn't be a problem just updating the level on all our boxes.

I'd assume most/all of our older machines are using gcc 4.8.4.

This might be a good time to test out our ansible scripts.

[seishun]

I would like to work on this, but I couldn't find documentation on how this whole thing works and how I can test it locally. I would be grateful if someone can point me in the right direction.

/cc @nodejs/build

[gibfahn]

@seishun old ansible scripts are in setup/, new ones are in ansible/, we're trying to move over to the new scripts, but they're not completely tested yet.

The README in the ansible directory should have the info you need to get started, and the scripts should be documented. If you run into any issues with it let us know.

[seishun]

@gibfahn I'm a complete noob here, would https://github.com/nodejs/build/blob/master/setup/TESTING_LOCALLY.md still work for testing new scripts?

[refack]

@seishun I tried to follow the guides once but got distracted... You doing it for the first time is a good chance to document missing pieces and hidden assumption, so it would be great if you open a doc PR or pass the info to me and I'll PR it.

[gibfahn]

@seishun in theory yes. Actually that document should really be ported over to ansible/.