brew install stan-math

[ankane]

Hi, it'd be great to add Stan Math (and eventually CmdStan) to Homebrew, so Mac users can install it with:

brew install stan-math

I've created a formula, but it requires patching, and Homebrew prefers patches to be accepted upstream. The two issues are:

1. Allowing system dependencies - #2659
2. --disable-new-dtags (in make/compiler_flags) errors with unknown option with Apple Clang

If these can be addressed, I think we can move things forward.

[WardBrian]

+1 to --disable-new-dtags needing to change, we also are patching it on the Conda version of cmdstan

[ankane]

Latest PR for 1: #2834