[PATCH v2] Revert "kbuild: Do not enable -Wimplicit-fallthrough for clang for now"

[Nick Desaulniers <ndesaulniers@google.com>]

This reverts commit e2079e93f562c7f7a030eb7642017ee5eabaaa10.

This has been fixed up over time thanks to the addition of "fallthrough"
pseudo-keyword in
commit 294f69e662d1 ("compiler_attributes.h: Add 'fallthrough' pseudo
keyword for switch/case use")

Link: https://github.com/ClangBuiltLinux/linux/issues/236
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Changes V1 -> V2:
* We actually want a revert, not a partial revert. v1 removed
  -Wimplicit-fallthrough outright, which we don't want. We still need
  cc-option for GCC < 7.

 Makefile | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index f353886dbf44..3edce16daede 100644
--- a/Makefile
+++ b/Makefile
@@ -777,11 +777,6 @@ else
 # These warnings generated too much noise in a regular build.
 # Use make W=1 to enable them (see scripts/Makefile.extrawarn)
 KBUILD_CFLAGS += -Wno-unused-but-set-variable
-
-# Warn about unmarked fall-throughs in switch statement.
-# Disabled for clang while comment to attribute conversion happens and
-# https://github.com/ClangBuiltLinux/linux/issues/636 is discussed.
-KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
 endif
 
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
@@ -905,6 +900,9 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 # warn about C99 declaration after statement
 KBUILD_CFLAGS += -Wdeclaration-after-statement
 
+# Warn about unmarked fall-throughs in switch statement.
+KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
+
 # Variable Length Arrays (VLAs) should not be used anywhere in the kernel
 KBUILD_CFLAGS += -Wvla
 
-- 
2.29.2.222.g5d2a92d10f8-goog