Which means we need *both* xcode cli tools and full xcode.
Document this weirdness, including the exact paths they should be at.
excerpt from terminal when running make_osx:
```
Warning: You are using macOS 10.14.
We (and Apple) do not provide support for this old version.
You will encounter build failures with some formulae.
Please create pull requests instead of asking for help on Homebrew's GitHub,
Twitter or any other official channels. You are responsible for resolving
any issues you experience while you are running this
old version.
==> Downloading https://ftp.gnu.org/gnu/coreutils/coreutils-9.0.tar.xz
Already downloaded: /Users/vagrant/Library/Caches/Homebrew/downloads/5744bb33344b6180adca9d909a87e830d55982a1b3229c61e9dc0e35cfacbf25--coreutils-9.0.tar.xz
Error: Xcode alone is not sufficient on Mojave.
Install the Command Line Tools for Xcode 11.3.1 from:
https://developer.apple.com/download/all/
```
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