Cleanup board and shield cmake code so that code duplication is reduced.
Before this commit, the code for verifying if BOARD or SHIELD user input
had changed was almost identical.
The common code has been made into a Zephyr extension function so that
all part of Zephyr build system can have a uniform way of checking if
sticky arguments has changed, and print user warning in a uniform way.
This also fixes an undiscovered flaw, where changing a shield is not
possible if a shield was defined at first CMake invocation, but in case
no shield had been specified at all, then build system would wrongly
allow specifying and changing shields, for example doing:
cmake -DBOARD=nrf52840dk_nrf52840 -DSHIELD=sparkfun_sara_r4 <sample>
cmake -DSHIELD=wnc_m14a2a
results correctly in:
> CMake Warning at zephyr/cmake/app/boilerplate.cmake:287 (message):
> The build directory must be cleaned pristinely when changing shields
and correctly keep existing SHIELD settings.
but doing:
cmake -DBOARD=nrf52840dk_nrf52840 <sample>
cmake -DSHIELD=sparkfun_sara_r4
cmake -DSHIELD=wnc_m14a2a
would not result in any warning, because `CACHED_SHIELD` was not
correctly checked in this case.
Changing shield is not a supported feature as it have unknown behavior.
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
7247412a9e