bug#29122: eshell passes ARGV[0] as full path to executable

[Yegor Timoshenko <yegortimoshenko@gmail.com>]

In M-x eshell.

Given this program in C in file example.c:

#include <stdio.h>
int main(int argc, char *argv[]) { puts(argv[0]); }

$ cc example.c
$ ./a.out
/home/chronos/a.out

This prints full path to the executable instead of passing the actual
ARGV[0]. In other shells, say bash, ./a.out will result in `./a.out`
being printed to stdout.

$ emacs-repository-get-version
cb185dfd0c227dda14de25d450d0d684e91cafb3
$ emacs-version
GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.24)
 of 2017-10-28

This is a recent build from master. This bug is also reproducible on
latest stable release, 25.3.