bug#34180: 27.0.50; argv[0] used incorrectly to find the .pdmp

[Daniel Colascione]

On 1/23/19 8:07 AM, Stefan Monnier wrote:
> Package: Emacs
> Version: 27.0.50
>
>
> Currently, the first .pdmp file that we try to load is found by adding
> ".pdmp" to argv[0].
> This has 2 problems:
>
> 1- It fails miserably if argv[0] is a name relative to $PATH since it
>     performs the lookup relative to $PWD instead, which is additionally
>     a security issue.
>
> 2- If the executable named by argv[0] is a symlink, it does not try to
>     follow the symlink in case the .pdmp is stored next to the
>     destination rather than next to the source.

Yep. We should definitely fix that. realpath on argv[0] seems like the 
right thing.