HW stack protection in ARMv8-M is implemented by default
with the built-in stack guard mechanism. Therefore, by
default all tests for ARMv8-M will use the built-in stack
overflow mechanism (CONFIG_BUILTIN_STACK_GUARD is set in
tests). However, we would like have some coverage on the
MPU stack guard mechanism for ARMv8-M. The added test case
manually disables BUILTIN_STACK_GUARD and enables the
MPU_STACK_GUARD option, to provide that test coverage.
Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>