New error: cleanup_makevar(old) : argument "RMU" is missing, with no default

@stevebronder I have no idea why but my guess is this is a Windows thing since you can’t reproduce it on ubuntu and I can’t on my mac. It seems like everyone reporting this is on Windows.

@bgoodri I know you said you were working on an RStan submission, so tagging you in case you haven’t seen this error that a lot of people are getting.