bug#20330: Do not capture build-time $PATH in 'emacs' binary

[Glenn Morris]

Ludovic Courtès wrote:

>>> +(setq exec-path nil)
>>
>> I'm not sure this is a good way to solve your issue.
>> Eg it will cause "Erase Customizations" on exec-path to set it to nil.
>
> OTOH, at startup, 'init_callproc_1' does:
>
>   Vexec_path = nconc2 (decode_env_path ("PATH", ""), Vexec_path);

I don't think that's relevant, is it?

It may make no real difference in practice, but I think I'd prefer to
see it set to a valid value. Eg whatever the bash shell's hard-coded
default is for PATH (/usr/local/bin:/bin:/usr/bin?) plus exec-directory.

(Also the setq-default seems superfluous, since exec-path is not buffer-local.)