kvm tools: build rbtree.o from source

Don't link the rbtree.o from kernel object tree, build
rbtree.o from source by ourselves.

Acked-by: Ingo Molnar <mingo@elte.hu>
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: WANG Cong <amwang@redhat.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

Makefile

@@ -45,9 +45,10 @@ OBJS    += disk/blk.o
 OBJS    += mptable.o
 OBJS    += threadpool.o
 OBJS    += irq.o
-OBJS    += ../../lib/rbtree.o
+OBJS    += rbtree.o
 OBJS    += util/rbtree-interval.o
 
+
 FLAGS_BFD=$(CFLAGS) -lbfd
 has_bfd := $(call try-cc,$(SOURCE_BFD),$(FLAGS_BFD))
 ifeq ($(has_bfd),y)
@@ -123,6 +124,8 @@ kvm-help.d: $(KVM_INCLUDE)/common-cmds.h
 
 $(OBJS):
 
+rbtree.o: ../../lib/rbtree.c
+	$(Q) $(CC) -c $(CFLAGS) $< -o $@
 %.o: %.c
 	$(E) "  CC      " $@
 	$(Q) $(CC) -c $(CFLAGS) $< -o $@