CONFIG_CC_STACKPROTECTOR v. armhf v3.13 mainline builds

[Kamal Mostafa]

The automatic builds of my v3.13-stable have always resulted in these
"all's well" emails:

        Subject:	Mainline Build v3.13.11-ckt29
        Subject:	Mainline Build v3.13.11-ckt30

Until the most recent release that I just uploaded, which got:

        Subject:	Mainline Build v3.13.11-ckt31 failed
        
        Build architecture status:
            binary-headers: good (rc=0)
            amd64: good (rc=0)
            i386: good (rc=0)
            armhf: failed (rc=2)    <<<===
            ppc64el: good (rc=0)

The armhf build[0] failed with:
        
        /home/kernel/COD/linux/arch/arm/boot/compressed/atags_to_fdt.c:96: undefined reference to `__stack_chk_fail'
        /home/kernel/COD/linux/arch/arm/boot/compressed/atags_to_fdt.c:96: undefined reference to `__stack_chk_guard'

But what's really weird is, when I go look at the previous 3.13 mainline
armhf build logs, I see that that error has ALWAYS been present[1]
despite the "all's well" emails!

Did the mainline builder somehow just recently gain the ability to
notice this failure?

Cking correctly identified the "stack_chk" thing as being enabled by
CONFIG_CC_STACKPROTECTOR.  (I can reproduce it with that, and not
without).

I _was_ worried that this problem might affect ubuntu-trusty also, but
now that I see its not even a new thing, I suppose that trusty is
probably okay.

Any thoughts on these topics will be much appreciated:

1. Why the builder suddenly notices this problem.
2. Why this problem occurs for armhf in 3.13 stable.

 -Kamal

[0]
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11-ckt31-trusty/BUILD.LOG.armhf

[1]
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11-ckt12-trusty/BUILD.LOG.armhf
...
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11-ckt30-trusty/BUILD.LOG.armhf