Add libs_tools support

Libraries used by qemu-<tools>

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Message-Id: 
diff --git a/Makefile b/Makefile
index afcafad..142a217 100644
--- a/Makefile
+++ b/Makefile
@@ -16,7 +16,7 @@
 
 VPATH=$(SRC_PATH):$(SRC_PATH)/hw
 
-LIBS+=-lz
+LIBS+=-lz $(LIBS_TOOLS)
 
 ifdef BUILD_DOCS
 DOCS=qemu-doc.html qemu-tech.html qemu.1 qemu-img.1 qemu-nbd.8