Index: xen-4.2.0-testing/tools/blktap/drivers/Makefile
===================================================================
--- xen-4.2.0-testing.orig/tools/blktap/drivers/Makefile
+++ xen-4.2.0-testing/tools/blktap/drivers/Makefile
@@ -4,7 +4,6 @@ include $(XEN_ROOT)/tools/Rules.mk
 IBIN         = blktapctrl tapdisk
 QCOW_UTIL    = img2qcow qcow2raw qcow-create
 
-CFLAGS   += -Werror
 CFLAGS   += -Wno-unused
 CFLAGS   += -I../lib
 CFLAGS   += $(CFLAGS_libxenctrl)
Index: xen-4.2.0-testing/Config.mk
===================================================================
--- xen-4.2.0-testing.orig/Config.mk
+++ xen-4.2.0-testing/Config.mk
@@ -24,7 +24,7 @@ SHELL     ?= /bin/sh
 
 # Tools to run on system hosting the build
 HOSTCC      = gcc
-HOSTCFLAGS  = -Wall -Werror -Wstrict-prototypes -O2 -fomit-frame-pointer
+HOSTCFLAGS  = -Wall -Werror -Wstrict-prototypes $(RPM_OPT_FLAGS)
 HOSTCFLAGS += -fno-strict-aliasing
 
 DISTDIR     ?= $(XEN_ROOT)/dist