[clang] [PS5][Driver] Allow `-T` to override `--default-script` (PR #116074)

[via cfe-commits]

https://github.com/bd1976bris approved this pull request.

LGTM. I would have preferred a simpler way of checking that there are no other occurrences of -T/--script/--default-script but couldn't think of anything.

I didn't notice that this was an upstream review initially. It would be worth waiting for approval from Jeremy.

https://github.com/llvm/llvm-project/pull/116074