seeking help fixing shells/fish4 on illumos

[Paolo Vincenzo Olivo <vins%NetBSD.org@localhost>]

Hi!

shells/fish4 currently contains a number of patches to allow it build on
illumos. I'm working with upstream to get these changes merged, but
there's still room for improvement. In particular, file type detection
is broken on illumos: the relevant code chunk is commented out [1], as
it uses `d_type' which SunOS dirent notoriously lacks. 

In other packages, I've used stat(2) alongisde  S_IS*** macros to
replace d_type on SunOS. But here, having no experience with rust, I
basically don't know where to start.

If someone is interested in getting this fixed, I'd appreciate some
help (feel free to to commit a working patch).