preserve -- in ARGS when it follows a non-option argument

[KristofferC]

Rebase of #37010 since that PR does not allow updating the author's branch.

This is a proposed fix for #37009. It removes manual processing of -- and relies on getopt() to handle it correctly. The expected behavior:

1. If -- appears before the first non-option argument, it forces the end of option processing and does not appear in ARGS.
2. If -- appears after a non-option argument, it is preserved in ARGS. This -- has no effect on option processing since it's already stopped on the first non-option argument.

[mkitti]

Interesting. This breaks how pyjulia installs PyCall.jl.

I'm a bit worried about how many other things this might break. Could we document this change better?

[MilesCranmer]

Here's a summary of the issue we are seeing. Say that I execute the following statement:

julia --startup-file=no test.jl -- arg1 arg2

where test.jl contains println(ARGS). Before, I would get:

["arg1", "arg2"]

But after this PR, I get:

["--", "arg1", "arg2"]

[MilesCranmer]

I wonder if there could simply be a warning displayed if -- is passed as a literal argument, at least for Julia 1.9? Perhaps a user could turn off the warning with some flag, indicating that they actually want to pass it. (It was quite hard to track down this error in PyJulia, I’m sure others will be hit as well.)

[KristofferC]

Having a NEWS entry for this is indeed a good idea.