Add support for illumos target

This change adds support for an illumos os target to libc.  Similar to the BSDs, there is a large deal of overlap (given the common history), so the 'solaris' directory was renamed to 'solarish' (it's the closest thing to an official term to refer to things descending from Solaris as well as Solaris).  There were also a number of missing definitions (as well as a couple missing functions) that have proved necessary for building a number of rust programs on illumos or Solaris.

Portions contributed by @papertigers .