doubt about 'bool is_executing'

[Gedare Bloom]

Hello all,

In most (all?) the SMP ports, we have in the CPU Context Control:
  bool is_executing;

This variable often is accessed through assembly language (i.e.,
during the context switch), using something like
ARCH_CONTEXT_CONTROL_IS_EXECUTING_OFFSET. Unfortunately, the 'bool'
type is not standard, or rather its size is implementation-defined.  I
think it is generally an 8-bit value though for us. I see that the
riscv port uses explicitly a uint32_t so that's nice.

I think we should replace 'bool' with uint8_t in the other ports that
are using byte-size accesses from assembly, just to be well-defined.
Most likely, this doesn't actually affect anything and I'm just a
little paranoid.

Gedare