[PATCH v2] kbuild: Require W=1 for -Wimplicit-fallthrough with clang

[Nathan Huckleberry]

Clang is updating to support -Wimplicit-fallthrough on C
https://reviews.llvm.org/D64838. Since clang does not
support the comment version of fallthrough annotations
this update causes an additional 50k warnings. Most
of these warnings (>49k) are duplicates from header files.

This patch is intended to be reverted after the warnings
have been cleaned up.

Signed-off-by: Nathan Huckleberry <nhuck@xxxxxxxxxx>
Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
---
Changes v1->v2
* Move code to preexisting ifdef
 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index a74ce2e3c33e..95973a1ee999 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -70,5 +70,6 @@ KBUILD_CFLAGS += -Wno-initializer-overrides
 KBUILD_CFLAGS += -Wno-format
 KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
+KBUILD_CFLAGS += $(call cc-option,-Wno-implicit-fallthrough)
 endif
 endif
-- 
2.23.0.rc1.153.gdeed80330f-goog