kbuild: fix single directory build

commit 3753af778d upstream.

Commit f110e5a250 ("kbuild: refactor single builds of *.ko") was wrong.

KBUILD_MODULES _is_ needed for single builds.

Otherwise, "make foo/bar/baz/" does not build module objects at all.

Fixes: f110e5a250 ("kbuild: refactor single builds of *.ko")
Reported-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Makefile

@@ -1890,6 +1890,8 @@ export KBUILD_SINGLE_TARGETS := $(addprefix $(extmod_prefix), $(single-no-ko))
 build-dirs := $(foreach d, $(build-dirs), \
 			$(if $(filter $(d)/%, $(KBUILD_SINGLE_TARGETS)), $(d)))
 
+KBUILD_MODULES := 1
+
 endif
 
 # Handle descending into subdirectories listed in $(build-dirs)