libnspr: add microblaze support

fixes autobuild failures

http://autobuild.buildroot.net/results/493/4932900522e87da84a47fbf2d796c2fbb3f7e741/build-end.log



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