configure: Make stack-protector test check both compile and link

Since we use the -fstack-protector argument at both compile and
link time in the build, we must check that it works with both
a compile and a link:
 * MacOSX only fails in the compile step, not linking
 * some gcc cross environments only fail at the link stage (if they
   require a libssp and it's not present for some reason)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1397232832-32301-1-git-send-email-peter.maydell@linaro.org
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
