Linux 5.3 compat: Makefile subdir-m no longer supported

Uses obj-m instead, due to kernel changes.

See LKML: Masahiro Yamada, Tue, 6 Aug 2019 19:03:23 +0900

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Dominic Pearson <dsp@technoanimal.net>
Closes openzfs#9169

.gitignore

@@ -63,3 +63,14 @@ cscope.*
 *.log
 venv
 
+#
+# Module leftovers
+#
+/module/avl/zavl.mod
+/module/icp/icp.mod
+/module/lua/zlua.mod
+/module/nvpair/znvpair.mod
+/module/spl/spl.mod
+/module/unicode/zunicode.mod
+/module/zcommon/zcommon.mod
+/module/zfs/zfs.mod

module/Makefile.in

@@ -1,11 +1,11 @@
-subdir-m += avl
-subdir-m += icp
-subdir-m += lua
-subdir-m += nvpair
-subdir-m += spl
-subdir-m += unicode
-subdir-m += zcommon
-subdir-m += zfs
+obj-m += avl/
+obj-m += icp/
+obj-m += lua/
+obj-m += nvpair/
+obj-m += spl/
+obj-m += unicode/
+obj-m += zcommon/
+obj-m += zfs/
 
 INSTALL_MOD_DIR ?= extra
 
@@ -60,13 +60,13 @@ modules_install:
 modules_uninstall:
 	@# Uninstall the kernel modules
 	kmoddir=$(DESTDIR)$(INSTALL_MOD_PATH)/lib/modules/@LINUX_VERSION@
-	list='$(subdir-m)'; for subdir in $$list; do \
-		$(RM) -R $$kmoddir/$(INSTALL_MOD_DIR)/$$subdir; \
+	list='$(obj-m)'; for objdir in $$list; do \
+		$(RM) -R $$kmoddir/$(INSTALL_MOD_DIR)/$$objdir; \
 	done
 
 distdir:
-	list='$(subdir-m)'; for subdir in $$list; do \
-		(cd @top_srcdir@/module && find $$subdir \
+	list='$(obj-m)'; for objdir in $$list; do \
+		(cd @top_srcdir@/module && find $$objdir \
 		-name '*.c' -o -name '*.h' -o -name '*.S' | \
 		xargs cp --parents -t @abs_top_builddir@/module/$$distdir); \
 	done