In SERVER-135540, the implementation of getTime() was updated to an architecture-agnostic absl clock call. We should:

1. Evaluate the compiled assembly to verify there are no function calls. (The current assembly implementation is just a basic instruction. We should not introduce additional overhead to ObservableMutex if possible.)
2. Run the observable mutex microbenchmarks with and without this change to see if there is any performance impact.
3. [Optionally] Ensure the new absl call works on other architectures (for example, s390x was having issues in HELP-101554). Possibly we should just return 0 on non-AArch64 and non-x86 builds?