utils: Fix gaining realtime scheduling with musl
sched_setscheduler() is implemented as a stub in musl that does nothing because Linux provides no way to set scheduling parameters per process.
Use pthread_setschedparam() to change the scheduling parameters of the threads instead.
(cherry picked from commit 5921be95)
Co-authored-by: Vlad Zahorodnii vlad.zahorodnii@kde.org