--enable-stack-protector for glibc, v4, now with arm

[Nix]

On 28 Feb 2016, nix@esperi.org.uk spake thusly:

> This is version 4 of the stack-protected glibc patch, incorporating all review
> comments to date (unless I missed some), and adding a degree of arm support
> (i.e. "I know nothing about the platform but the tests passed").

So... other than the changelog, is there anything else I need to do to
get review of the trickier parts of this? I've exhausted all the
platforms I have access to and fixed all regressions on such platforms,
but am happy to test/fix on more if people give me access to them.

-- 
NULL && (void)