The previous SMP multitasking start assumed that the initial heir thread of a
processor starts execution in _Thread_Handler(). The _Thread_Handler() sets
the interrupt state explicitly by _ISR_Set_level() before it calls the thread
entry. Under certain timing conditions, processors may perform an initial
context switch to a thread which already executes its thread body (see
smptests/smpstart01). In this case, interrupts are disabled after the context
switch on targets which do not save/restore the interrupt state during a
context switch (aarch64, arm, and riscv).
Close#4627.