Feature/845 makefile macos (#846)
Feature/845 makefile macos (#846)

* xattr logic for macos

* macos xattr logic

* logic cleanup; tested

* fix comments

Co-authored-by: Mitzi Morris <301ed13681a1ba338b621f8389e6802c9117fe33@thistle.local>
Co-authored-by: rok-cesnovar <8bec8713d4ced84fdc49921cadf08736798069be@fri.uni-lj.si>
stan-dev/cmdstan,stan-dev/cmdstan,stan-dev/cmdstan,stan-dev/cmdstan