aufs stdalone: for v5.3, new headers_install scheme

By the commits in mainline,
59b2bd05f5f4 2019-06-15 kbuild: add 'headers' target to build up uapi headers in usr/include
d5470d14431e 2019-06-15 kbuild: re-implement Makefile.headersinst without recursion
555187a8791d 2019-06-15 kbuild: simplify scripts/headers_install.sh

the scheme changed a little bit.  Since aufs standalone GIT generates
and installs aufs_type.h to userspace, simply follow the new scheme.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Makefile

@@ -42,10 +42,9 @@ fs/aufs/aufs.ko:
 	@echo ${EXTRA_CFLAGS}
 	${MAKE} ${MakeMod} modules
 
-usr/include/linux/aufs_type.h: d = $(shell echo ${CURDIR} | cut -c2-)
-usr/include/linux/aufs_type.h:
-	${MAKE} -rR -C ${KDIR} \
-		-f scripts/Makefile.headersinst \
-		-f Makefile \
-		obj=${d}/include/uapi/linux dst=${d}/usr/include/linux
+usr/include/linux/aufs_type.h: ${KDIR}/scripts/headers_install.sh \
+				${CURDIR}/include/uapi/linux/aufs_type.h
+	${MAKE} -C ${KDIR} scripts_unifdef
+	mkdir -p $(dir $@)
+	cd ${KDIR} && $^ ${CURDIR}/$@
 	test -s $@