cmake: Introduce zephyr_check_compiler_flag()

zephyr_check_compiler_flag is introduced to resolve
https://github.com/zephyrproject-rtos/zephyr/issues/5633



The time spent when invoking CMake is halved with a warm cache.

See the API documentation for details.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>