Comment 11 for bug 1816841

@Michael D.: Heinz has already created a commit with my patch applied. He added an #ifdef (see his comment above) and removed the 'isEpicsThread' member (except from os/Linux/osdThread.h from where it should be removed as well). I had suggested this step as it then allows non-Epics threads to user epicsThreadSetPriority().

I'll do this removal shortly and submit a PR on github.