qemu-user: $0 incorrectly always reports absolute path

We just ran into an issue with the Perl package on Debian/m68k when being built with qemu-user [1].

The problem can be boiled down to qemu-user always reporting absolute paths for the shell variable $0 no matter on how the command was invoked.

A simple reproducer is this:

On normal system (no emulation):

root@nofan:~> sh -c 'echo $0'
sh
root@nofan:~>

On qemu-user:

(sid-m68k-sbuild)root@nofan:/# sh -c 'echo $0'
/bin/sh
(sid-m68k-sbuild)root@nofan:/#

> [1] https://lists.debian.org/debian-68k/2019/07/msg00007.html