--- xen-4.2.2/tools/Makefile.orig	2013-05-30 03:04:27.029917107 +0200
+++ xen-4.2.2/tools/Makefile	2013-05-30 03:04:53.093610079 +0200
@@ -187,6 +187,7 @@
 		source=.; \
 	fi; \
 	cd qemu-xen-dir; \
+	env -u CFLAGS \
 	$$source/configure --enable-xen --target-list=i386-softmmu \
 		--source-path=$$source \
 		--extra-cflags="-I$(XEN_ROOT)/tools/include \