It turns out that 'check_compiler_flag' has not been working for flags
that start with -Wno-. This has caused old compilers to accidentally
use flags that they do not support.
To fix this we check for compatibility with the appropriate -W flag
instead and infer the -Wno- compatibility from this check.
The root cause of this problem is explained well here:
https://github.com/zephyrproject-rtos/zephyr/pull/18922#discussion_r321537098
Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
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