lib/Makefile.in: fix make clean exit

lib/Makefile.in

@@ -16,7 +16,7 @@ default: normal
 
 clean:
 	-+@cd bdlib && $(MAKE) clean
-	-+@[ -n "${LIBELF_BUNDLED}" ] && [ -f libelf/Makefile && \
+	-+@[ -n "${LIBELF_BUNDLED}" ] && [ -f libelf/Makefile ] && \
 	    cd libelf && $(MAKE) clean
 	@rm -f *.a