diff -dur -x '*~' xen-4.1.2.orig/Config.mk xen-4.1.2/Config.mk
--- xen-4.1.2.orig/Config.mk	2011-10-20 19:06:04.000000000 +0200
+++ xen-4.1.2/Config.mk	2012-09-20 08:44:53.000000000 +0200
@@ -14,7 +14,7 @@
 
 # Tools to run on system hosting the build
 HOSTCC      = gcc
-HOSTCFLAGS  = -Wall -Werror -Wstrict-prototypes -O2 -fomit-frame-pointer
+HOSTCFLAGS  = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
 HOSTCFLAGS += -fno-strict-aliasing
 
 DISTDIR     ?= $(XEN_ROOT)/dist
--- xen-4.4.1/tools/blktap2/drivers/Makefile~	2014-09-02 08:20:19.000000000 +0200
+++ xen-4.4.1/tools/blktap2/drivers/Makefile	2014-12-13 19:19:17.070688454 +0100
@@ -4,7 +4,6 @@
 LOCK_UTIL  = lock-util
 INST_DIR   = $(sbindir)
 
-CFLAGS    += -Werror
 CFLAGS    += -Wno-unused
 CFLAGS    += -fno-strict-aliasing
 CFLAGS    += -I$(BLKTAP_ROOT)/include -I$(BLKTAP_ROOT)/drivers