package/kvm-unit-tests: fix build with SSP

Add a patch to correct a typo in the Makefile, so -fno-stack-protector /
-fno-stack-protector-all are really used.  With this applied, kvm-unit-tests
will always be built without SSP as intented by upstream.  This will fix the
build on ppc64 with SSP that started to fail for an unknown reason since
November 27th.

Moreover, the Arch Linux workaround could also be removed in a follow-up
patch.

Fixes:
 - http://autobuild.buildroot.org/results/ad689b08173548af21dd1fb0e827fd561de6dfef



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>