add special linker scripts, to disable lazy loading of symbols and to make relocations read-only, security enhancement, idea seen in sabotage linux

mk/vars.mk

@@ -85,6 +85,8 @@ TARGET_LDFLAGS:=	-L$(STAGING_TARGET_DIR)/lib -L$(STAGING_TARGET_DIR)/usr/lib \
 			-Wl,-O2 -Wl,-rpath -Wl,/usr/lib \
 			-Wl,-rpath-link -Wl,${STAGING_TARGET_DIR}/usr/lib \
 			$(ADK_TARGET_ABI_LDFLAGS) $(TARGET_CFLAGS_ARCH)
+# security optimization, see http://www.akkadia.org/drepper/dsohowto.pdf
+TARGET_LDFLAGS+=	-Wl,-z,relro,-z,now
 
 ifneq ($(ADK_NATIVE),)
 TARGET_CPPFLAGS:=