Enable `TRACY_TIMER_FALLBACK` for libTracyClient
This fallback is most likely to kick in on VM's that may not have
support for the rdtsc instruction.
The loss in timer fidelity can be pretty severe (8 ns -> 15.6 ms)
but we pack lots of other metadata into our traces, so it can still
be useful to run with the fallback (and forcefully crashing the
application as Tracy does now is just not the Julian way to
communicate a hard error anyway)
