override plugin for LTTng-UST. This can be useful in cases where direct
hardware access is available for architecture-specific clocks, and where
it should be used rather than the Linux kernel Monotonic clock.
+
+When using LTTng-tools keep in mind that lttng-sessiond uses lttng-ust's clock
+definition and functions. Thus LTTNG_UST_CLOCK_PLUGIN needs to be defined when
+launching lttng-sessiond.