[PATCH] kbuild: Unbreak cleaning external module build directory

[Bart Van Assche <bvanassche@acm.org>]

Avoid that "$(MAKE) -C $(KDIR) M=$(PWD) clean" triggers the following
error message when invoked from inside the Makefile of an external
kernel module:

rm: cannot remove 'System.map': Permission denied
make[1]: *** [clean] Error 1

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Arnaud Lacombe <lacombar@gmail.com>
Cc: Nick Bowler <nbowler@elliptictech.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Michal Marek <mmarek@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 9f6ca12..46b9be5 100644
--- a/Makefile
+++ b/Makefile
@@ -1252,7 +1252,7 @@ scripts: ;
 endif # KBUILD_EXTMOD
 
 clean: $(clean-dirs)
-	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
+	$(Q)$(if $(KBUILD_EXTMOD),,$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean)
 	$(call cmd,rmdirs)
 	$(call cmd,rmfiles)
 	@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
-- 
1.7.10.4