nixos/stage-1: Make find-libs not choke on dynamic linker being in DT_NEEDED

find-libs is currently choking when it finds the dynamic linker
as a DT_NEEDED dependency (from glibc) and bails out like this
(as glibc doesn't have a RPATH):

Couldn't satisfy dependency ld-linux-x86-64.so.2

Actually the caller of find-libs ignores the exit status, so the issue
almost always goes unnoticed and happens to work by chance. But
additionally what happens is that indirect .so dependencies are
left out from the dependency closure calculation, which breaks
latest cryptsetup as libssl.so isn't found anymore.