libnss: fix build without int128

Patch retrieved from upstream, more info here:
https://bugzilla.mozilla.org/show_bug.cgi?format=default&id=1459739

Fixes:
 - http://autobuild.buildroot.net/results/093113829d7ce19d578a920e76caa10822774139



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>