kbuild: avoid duplicate warning options

Some warning options are disabled at one place and then conditionally
re-enabled later in scripts/Makefile.extrawarn.

For consistency, rework this file so each of those warnings only
gets etiher enabled or disabled based on the W= flags but not both.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.extrawarn

@@ -56,20 +56,12 @@ KBUILD_CFLAGS += -Wno-pointer-sign
 # globally built with -Wcast-function-type.
 KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
 
-# disable stringop warnings in gcc 8+
-KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
-
 # We'll want to enable this eventually, but it's not going away for 5.7 at least
 KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow)
 
 # Another good warning that we'll want to enable eventually
 KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
 
-# Enabled with W=2, disabled by default as noisy
-ifdef CONFIG_CC_IS_GCC
-KBUILD_CFLAGS += -Wno-maybe-uninitialized
-endif
-
 # The allocators already balk at large sizes, so silence the compiler
 # warnings for bounds checks involving those possible values. While
 # -Wno-alloc-size-larger-than would normally be used here, earlier versions
@@ -96,8 +88,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
 # Warn if there is an enum types mismatch
 KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
 
-KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
-
 # backward compatibility
 KBUILD_EXTRA_WARN ?= $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)
 
@@ -122,11 +112,6 @@ KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable)
 KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
 KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned)
 KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
-# The following turn off the warnings enabled by -Wextra
-KBUILD_CFLAGS += -Wno-missing-field-initializers
-KBUILD_CFLAGS += -Wno-sign-compare
-KBUILD_CFLAGS += -Wno-type-limits
-KBUILD_CFLAGS += -Wno-shift-negative-value
 
 KBUILD_CPPFLAGS += -Wundef
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
@@ -135,9 +120,12 @@ else
 
 # Some diagnostics enabled by default are noisy.
 # Suppress them by using -Wno... except for W=1.
+KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
+KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
+KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
 
 ifdef CONFIG_CC_IS_CLANG
-KBUILD_CFLAGS += -Wno-initializer-overrides
 # Clang before clang-16 would warn on default argument promotions.
 ifneq ($(call clang-min-version, 160000),y)
 # Disable -Wformat
@@ -151,7 +139,6 @@ ifeq ($(call clang-min-version, 120000),y)
 KBUILD_CFLAGS += -Wformat-insufficient-args
 endif
 endif
-KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
@@ -173,8 +160,25 @@ KBUILD_CFLAGS += -Wtype-limits
 KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
 KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
 
+ifdef CONFIG_CC_IS_CLANG
+KBUILD_CFLAGS += -Winitializer-overrides
+endif
+
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2
 
+else
+
+# The following turn off the warnings enabled by -Wextra
+KBUILD_CFLAGS += -Wno-missing-field-initializers
+KBUILD_CFLAGS += -Wno-type-limits
+KBUILD_CFLAGS += -Wno-shift-negative-value
+
+ifdef CONFIG_CC_IS_CLANG
+KBUILD_CFLAGS += -Wno-initializer-overrides
+else
+KBUILD_CFLAGS += -Wno-maybe-uninitialized
+endif
+
 endif
 
 #
@@ -196,6 +200,11 @@ KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
 
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
 
+else
+
+# The following turn off the warnings enabled by -Wextra
+KBUILD_CFLAGS += -Wno-sign-compare
+
 endif
 
 #