minios: _chk_fail and _chk canaries for minios and newlib

Add __stack_chk_fail to mini-os and __sprintf_chk __fprintf_chk to
newlib, to cope with ocaml runtimes compiled with -fstack-protector.

From: "George S. Coker, II" <gscoker@alpha.ncsc.mil>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

extras/mini-os/lib/stack_chk_fail.c

@@ -0,0 +1,8 @@
+#include <kernel.h>
+#include <console.h>
+
+void __stack_chk_fail(void)
+{
+    printk("stack smashing detected\n");
+    do_exit();
+}

stubdom/Makefile

@@ -91,6 +91,7 @@ newlib-$(NEWLIB_VERSION).tar.gz:
 newlib-$(NEWLIB_VERSION): newlib-$(NEWLIB_VERSION).tar.gz
 	tar xzf $<
 	patch -d $@ -p0 < newlib.patch
+	patch -d $@ -p0 < newlib-chk.patch
 	touch $@
 
 NEWLIB_STAMPFILE=$(CROSS_ROOT)/$(GNU_TARGET_ARCH)-xen-elf/lib/libc.a