libsigsegv: add support for Nios II

This commit adds a patch to libsigsegv that indicates the stack
direction on Nios II, which is needed for libsigsegv to build properly
on this architecture.

Fixes:

  http://autobuild.buildroot.org/results/943/9436c3208cfeee9bd3bc211df007e745fe13c2c2/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>