hylia: test for CLOCK_MONOTONIC_RAW before using it

source/modules/hylia/link/ableton/platforms/linux/Clock.hpp

@@ -49,7 +49,9 @@ public:
 };
 
 using ClockMonotonic = Clock<CLOCK_MONOTONIC>;
+#ifdef CLOCK_MONOTONIC_RAW
 using ClockMonotonicRaw = Clock<CLOCK_MONOTONIC_RAW>;
+#endif
 
 /* Warning: the realtime clock can be subject to time change.
  * One of the hard requirements of Ableton Link is that the clock must be