kbuild: clear KBUILD_MODULES in top Makefile if CONFIG_MODULES=n

Do not try to build any module-related artifacts when CONFIG_MODULES
is disabled.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1724,6 +1724,10 @@ build-dirs := $(foreach d, $(build-dirs), \
 
 endif
 
+ifndef CONFIG_MODULES
+KBUILD_MODULES :=
+endif
+
 # Handle descending into subdirectories listed in $(build-dirs)
 # Preset locale variables to speed up the build process. Limit locale
 # tweaks to this spot to avoid wrong language settings when running

scripts/Makefile.build

@@ -77,7 +77,7 @@ ifdef need-builtin
 builtin-target := $(obj)/built-in.a
 endif
 
-ifeq ($(CONFIG_MODULES)$(need-modorder),y1)
+ifdef need-modorder
 modorder-target := $(obj)/modules.order
 endif