kbuild: refactor single builds of *.ko

Remove the potentially invalid modules.order instead of using
the temporary file.

Also, KBUILD_MODULES is don't care for single builds. No need to
cancel it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1782,6 +1782,8 @@ modules modules_install:
 	@echo >&2 '***'
 	@exit 1
 
+KBUILD_MODULES :=
+
 endif # CONFIG_MODULES
 
 # Single targets
@@ -1808,18 +1810,12 @@ $(single-ko): single_modpost
 $(single-no-ko): descend
 	@:
 
-ifeq ($(KBUILD_EXTMOD),)
-# For the single build of in-tree modules, use a temporary file to avoid
-# the situation of modules_install installing an invalid modules.order.
-MODORDER := .modules.tmp
-endif
-
+# Remove MODORDER when done because it is not the real one.
 PHONY += single_modpost
 single_modpost: $(single-no-ko) modules_prepare
 	$(Q){ $(foreach m, $(single-ko), echo $(extmod_prefix)$m;) } > $(MODORDER)
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
-
-KBUILD_MODULES := 1
+	$(Q)rm -f $(MODORDER)
 
 export KBUILD_SINGLE_TARGETS := $(addprefix $(extmod_prefix), $(single-no-ko))
 
@@ -1829,10 +1825,6 @@ 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