fix "make install" with relative PREFIX

Makefile.in

@@ -426,7 +426,7 @@ ifeq ($(HAVE_SHARED),y)
 	$(INSTALL) -d $(PREFIX)$(RUNTIME_PREFIX)lib
 	$(INSTALL) -m 644 lib/lib*-$(VERSION).so \
 		$(PREFIX)$(RUNTIME_PREFIX)lib
-	cd lib && $(TAR) -cf - *.so.* | $(TAR) -xf - -C $(PREFIX)$(RUNTIME_PREFIX)lib
+	(cd lib && $(TAR) -cf - *.so.*) | $(TAR) -xf - -C $(PREFIX)$(RUNTIME_PREFIX)lib
 	@if [ -x lib/$(UCLIBC_LDSO_NAME)-$(VERSION).so ] ; then \
 		set -e; \
 		$(SHELL_SET_X); \