Fix build with zig 0.10.0-dev.1946+6f4343b61

I wasn't planning on (publicly) keeping up with Zig master before the
next release, but it's looking like 0.10 will mainly focus on the new
stage2 compiler and there might not be any significant language/stdlib
changes. If that's the case, might as well pull in this little change in
order to increase chances of ncdu working out of the box when 0.10 is
out.