k_thread_abort() pends PendSV with SCB->ICSR |= PENDSVSET, the third
such site after arch_swap() and z_arm_exc_exit(). ICSR's writable bits
are write-one-to-set or write-one-to-clear and writing zero is a no-op,
so the read-modify-write is equivalent to a plain store while also
writing back a stale snapshot of the other write-one bits.
This path is not hot, so the motivation is consistency and dropping
that stale write-back rather than the saved access. The SHCSR update
immediately below stays a read-modify-write: its bits are ordinary
read/write ones that have to be preserved.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
8b93109f26