When committing rGdba420bc05ae, I missed that a darwin-specific change had been recently introduced into llvm-cxxfilt (see rGe84468c1f145), which my change ignored and consequently broke the darwin build bot. This change fixes this issue as well as improving naming/commenting of things related to this point so that people are less likely to run into the same issue as I did.
I have landed this patch already as rG281539053238 to unbreak the build bot, but would appreciate a post-commit review.
This line should have llvm-cxxfilt -n. I've fixed this in rG01d8bb49.