[Do Not Merge] Add OSX to Travis config

[zware]

Testing feasibility of adding osx back to the Travis config. This should not be merged until it's done a few builds to get an idea of how it affects us.

[AraHaan]

Uh the Travis build can take a lot longer than it would with Doozer.io. You guys might need to look into it as on OSX you can tell it to use gcc or clang for building cpython. For more information on setting it up you are free to look at my copy I did to try to bring C++ 14 to the OSX builds which ends up failing completely. It is located at https://github.com/AraHaan/bin2c/blob/master/.doozer.json.

The Doozer.io homepage is at https://doozer.io/ as well.

[refi64]

FYI instead of bogus commits, you can close and re-open the PR in order to restart a Travis build.

[AraHaan]

Come to look at it the Linux builds except for the coverage ones could be sped up a lot too with Doozer.io and then only use Travis for coverage.

With that said I will cook up an .doozer.json file for cpython for the normal and doc builds for both OSX and Linux. But on Linux I will not bother apt getting the latest gcc unless cpython recommends a version newer than the default one they ship.

[zware]

@AraHaan This is not the place to discuss replacing Travis. If you're interested in that, either open an issue in python/core-workflow or send a message to the core-workflow list.

@kirbyfan64 Not in this case, since the build was skipped due to not having any code changes.

[zware]

Superseded by GH-1846.