OpenBSD, llvm, and go all have six month cadences.
Go 2.0 will probably be a different story, assuming it ever comes out, but I have a hard time believing the devs will release anything that won't be fixable using the "go fix" tool.
You cannot compare an OS, or in general any product which is "complete by itself" (browsers), with a compiler which is then used to _make_ the end product. Your source depends on it, and as it grows it just becomes increasingly hard to keep up.
Rolling releases are /also/ a tradeoff. I'm not particularly pleased with llvm in this case. I genuinely prefer semantic releases, and yes, even the python2->3 strategy in this context.