kbuild: include scripts/Makefile.* only when relevant CONFIG is enabled

Currently, the top Makefile includes all of scripts/Makefile.<feature>
even if the associated CONFIG option is disabled.

Do not include unneeded Makefiles in order to slightly optimize the
parse stage.

Include $(include-y), and ignore $(include-).
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -745,9 +745,6 @@ endif
 KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)
 KBUILD_CFLAGS	+= $(call cc-option,-fno-allow-store-data-races)
 
-include scripts/Makefile.kcov
-include scripts/Makefile.gcc-plugins
-
 ifdef CONFIG_READABLE_ASM
 # Disable optimizations that make assembler listings hard to read.
 # reorder blocks reorders the control in the function
@@ -948,10 +945,15 @@ ifdef CONFIG_RETPOLINE
 KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
 endif
 
-include scripts/Makefile.kasan
-include scripts/Makefile.extrawarn
-include scripts/Makefile.ubsan
-include scripts/Makefile.kcsan
+# include additional Makefiles when needed
+include-y			:= scripts/Makefile.extrawarn
+include-$(CONFIG_KASAN)		+= scripts/Makefile.kasan
+include-$(CONFIG_KCSAN)		+= scripts/Makefile.kcsan
+include-$(CONFIG_UBSAN)		+= scripts/Makefile.ubsan
+include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
+include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
+
+include $(addprefix $(srctree)/, $(include-y))
 
 # Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
 KBUILD_CPPFLAGS += $(KCPPFLAGS)

scripts/Makefile.kcov

 # SPDX-License-Identifier: GPL-2.0-only
-ifdef CONFIG_KCOV
-
 kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC)	+= -fsanitize-coverage=trace-pc
 kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS)	+= -fsanitize-coverage=trace-cmp
 kcov-flags-$(CONFIG_GCC_PLUGIN_SANCOV)		+= -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so
 
 export CFLAGS_KCOV := $(kcov-flags-y)
-
-endif

scripts/Makefile.kcsan

 # SPDX-License-Identifier: GPL-2.0
-ifdef CONFIG_KCSAN
-
 # GCC and Clang accept backend options differently. Do not wrap in cc-option,
 # because Clang accepts "--param" even if it is unused.
 ifdef CONFIG_CC_IS_CLANG
@@ -15,5 +13,3 @@ CFLAGS_KCSAN := -fsanitize=thread \
 	$(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \
 	$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1)) \
 	$(call cc-param,tsan-distinguish-volatile=1)
-
-endif # CONFIG_KCSAN

scripts/Makefile.ubsan

 # SPDX-License-Identifier: GPL-2.0
-ifdef CONFIG_UBSAN
-
 ifdef CONFIG_UBSAN_ALIGNMENT
       CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
 endif
@@ -26,4 +24,3 @@ endif
       # -fsanitize=* options makes GCC less smart than usual and
       # increase number of 'maybe-uninitialized false-positives
       CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)
-endif