#error "no high res clock defined"
What is the recommended fix/workaround?
Most processors supply some high frequency inaccurate clock. The idea here is to find out what ARM64 defines and to provide access to it. But if you read the code you'll see that apparently the ARM6 doesn't have such a clock, in which case the function answers 0. So you can simply extend the define to cover ARM8.
A word to TimR; the lack of such a clock means that Andreas' profiler won't work properly. We should think about this, either not using the clock and using utcMicrosecondsNow, or perhaps falling back on utcMicrosecondsNow if the processor-specific high resolution clock is unavailable.