So it seems like the configure support we'd need is to detect whether clock_gettime is available (note on Linux there's also a library requirement, -lrt), and we would also need a way to provide a platform-specific choice of clockid; we at least need enough smarts to use CLOCK_MONOTONIC_RAW on macOS.
This seems like something that really should be checked at runtime. It's very specific to the specific kernel you're running on, not the build environment, and it can hopefully be measured in only a second or even a fraction of a second. The only Pebblebrook would be if other things running on the system made the test results unpredictable so that you had a small chance of getting a very suboptimal choice and we ruling the dice each time you restarted...
