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If the particular version of clang a user has doesn't enable
-Werror=unknown-warning-option by default, even though it is the
default[1], then make sure to pass the option to the Kconfig cc-option
command so that testing options from Kconfig files works properly.
Otherwise, depending on the default values setup in the clang toolchain
we will silently assume options such as -Wmaybe-uninitialized are
supported by clang, when they really aren't.

A compilation issue only started happening for me once commit
589834b3 ("kbuild: Add -Werror=unknown-warning-option to
CLANG_FLAGS") was applied on top of commit b303c6df ("kbuild:
compute false-positive -Wmaybe-uninitialized cases in Kconfig"). This
leads kbuild to try and test for the existence of the
-Wmaybe-uninitialized flag with the cc-option command in
scripts/Kconfig.include, and it doesn't see an error returned from the
option test so it sets the config value to Y. Then the ...