[sudo-workers] Improve stack smashing protector check

[Todd C. Miller]

On Wed, 28 Oct 2015 13:58:21 -0000, Vicente Olivert Riera wrote:

> The attached patch is an improvement for the stack smashing protector
> check in the configure.ac file.

This is a good idea but it needs to use AC_COMPILE_IFELSE instead
of calling CC directly.  I'll take a stab at this for the upcoming
1.8.16 release.

 - todd