kbuild: add -Wundef to KBUILD_CPPFLAGS for W=1 builds
The use of an undefined macro in an #if directive is warned, but only in *.c files. No warning from other files such as *.S, *.lds.S. Since -Wundef is a preprocessor-related warning, it should be added to KBUILD_CPPFLAGS instead of KBUILD_CFLAGS. My previous attempt [1] uncovered several issues. I could not finish fixing them all. This commit adds -Wundef to KBUILD_CPPFLAGS for W=1 builds in order to block new breakages. (The kbuild test robot tests with W=1) We can fix the warnings one by one. After fixing all of them, we can make it default in the top Makefile, and remove -Wundef from KBUILD_CFLAGS. [1]: https://lore.kernel.org/all/20221012180118.331005-2-masahiroy@kernel.org/ Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
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