[pushed] Fix sim build failure

[Mike Frysinger]

On 22 Apr 2021 19:51, Tom Tromey wrote:
> On x86-64 Fedora 32, the sim was failing to build.
> sim_events_schedule was passing a 'dummy' argument to
> sim_events_schedule_vtracef, which caused an error because the format
> parameter was NULL.  However, removing this dummy argument caused an
> error because too few arguments were being passed -- catch 22.
> 
> This patch fixes the build problem by using sim_events_schedule_tracef
> instead.

thx!
-mike