[PATCH for-4.19] tools/xs-clients: Fix `make clean` rule

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Prior to the split, "the clients" used tools/xenstored/Makefile.common whose
clean rule includes *.o whereas after the split, the removal of *.o was lost
by virtule of not including Makefile.common any more.

This is the bug behind the following build error:

  make[2]: Entering directory '/local/xen.git/tools/xs-clients'
  gcc     xenstore_client.o    (snip)
  /usr/bin/ld: xenstore_client.o: relocation R_X86_64_32S against `.rodata' can 
not be used when making a PIE object; recompile with -fPIE
  /usr/bin/ld: failed to set dynamic section sizes: bad value
  collect2: error: ld returned 1 exit status
  make[2]: *** [Makefile:35: xenstore] Error 1

which was caused by `make clean` not properly cleaning the tree as I was
swapping between various build containers.

Switch to a plain single-colon clean rule.

Fixes: 5c293058b130 ("tools/xenstore: move xenstored sources into dedicated 
directory")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

For 4.19.  It's a minor build system corner case, but is also very safe too.

Ultimately it needs backporting to 4.18 too.
---
 tools/xs-clients/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/xs-clients/Makefile b/tools/xs-clients/Makefile
index 4e78d365e0df..5415c441920a 100644
--- a/tools/xs-clients/Makefile
+++ b/tools/xs-clients/Makefile
@@ -38,8 +38,8 @@ xenstore-control: xenstore_control.o
        $(CC) $(LDFLAGS) $^ $(LDLIBS) -o $@ $(APPEND_LDFLAGS)
 
 .PHONY: clean
-clean::
-       $(RM) $(TARGETS) $(DEPS_RM)
+clean:
+       $(RM) *.o $(TARGETS) $(DEPS_RM)
 
 .PHONY: distclean
 distclean: clean
-- 
2.39.2