In commit b2d1eb717b ("generic: 5.15: enable Werror by default for
kernel compile") CONFIG_WERROR=y was enabled and all warnings/errors
reported with GCC 12 were fixed.
Keeping this in sync with past/future GCC versions is going to be uphill
battle, so lets introduce new KERNEL_WERROR config option, enable it by
default only for tested/known working combinations and on buildbots.
References: #12687
Signed-off-by: Petr Štetiar <ynezz@true.cz>