vboot2: Use the right set of compiler flags for building vboot libraries

This make it pass through -fno-stack-protector, and also uses
libverstage fields consistently.
verstage is for 'stage' stuff, libverstage for all the vboot logic.

Change-Id: I3032e072414bed52effd2dc5057896781ad562c6
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/10174
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
diff --git a/src/vendorcode/google/chromeos/vboot2/Makefile.inc b/src/vendorcode/google/chromeos/vboot2/Makefile.inc
index e9377b2..fe1d237 100644
--- a/src/vendorcode/google/chromeos/vboot2/Makefile.inc
+++ b/src/vendorcode/google/chromeos/vboot2/Makefile.inc
@@ -50,7 +50,8 @@
 endif # CONFIG_SEPARATE_VERSTAGE
 
 VB2_LIB = $(obj)/external/vboot_reference/vboot_fw20.a
-VBOOT_CFLAGS += $(patsubst -I%,-I$(top)/%,$(filter-out -include $(src)/include/kconfig.h, $(CPPFLAGS_verstage)))
+VBOOT_CFLAGS += $(patsubst -I%,-I$(top)/%,$(filter-out -include $(src)/include/kconfig.h, $(CPPFLAGS_libverstage)))
+VBOOT_CFLAGS += $(CFLAGS_libverstage)
 VBOOT_CFLAGS += $(libverstage-c-ccopts)
 VBOOT_CFLAGS += -include $(top)/src/include/kconfig.h -Wno-missing-prototypes
 VBOOT_CFLAGS += -DVBOOT_DEBUG