Posix: Do not treat arguments as `FilePath`

[mmhat]

Fixes #319

[tomjaguarpaw]

This looks pretty plausible to me, but I'm not an expert with the low level details. There are various people who are better qualified. Perhaps one of them can chime in.

@bgamari @hasufell @snoyberg @Mistuke (or someone else?)

[hasufell]

There are two differences:

1. withFilePath uses getFileSystemEncoding, withCString uses getForeignEncoding
2. withFilePath checks for interior nulls now (not sure since which base version) and barfs out in case it finds any

Tbh, all of those s*ck. But that's another discussion: https://github.com/haskell/process/issues/252

[mmhat]

2. withFilePath checks for interior nulls now (not sure since which base version) and barfs out in case it finds any

I think it is since base-4.18.0.0 (GHC 9.6.1).

If there are no further objections: Who is willing to merge this?

[tomjaguarpaw]

OK, released as https://hackage.haskell.org/package/process-1.6.22.0. Thanks @mmhat!