Add -Werror=format-security

Security hardening: don't allow code to compile which
uses format strings in an inappropriate way.  Make format
string compiler warnings into errors.

Change-Id: I1461dad589a2416420fd84ccf765983e859eea8a
diff --git a/core/combo/TARGET_linux-arm.mk b/core/combo/TARGET_linux-arm.mk
index 2bc91c9..8c3fd3c 100644
--- a/core/combo/TARGET_linux-arm.mk
+++ b/core/combo/TARGET_linux-arm.mk
@@ -98,6 +98,7 @@
 			-funwind-tables \
 			-fstack-protector \
 			-Wa,--noexecstack \
+			-Werror=format-security \
 			-fno-short-enums \
 			$(arch_variant_cflags) \
 			-include $(android_config_h) \