In glibc, getauxval(3) is a monster API that keeps growing additional
heads and tentacles.  Exporting a tiny version of it to userland is
worrying.

When the real problem here is a tiny little check to use done only
internal to only our libc, and therefore why not use an OpenBSD private
interface.  This means it could be built upon the assumption "this is an
openbsd binary", and use a sysctl interface.  After 2 months, there will
be only one kind of binary.