alanc, I filed two bugs and a pull request for squid's ModDevPoll backend for #Solaris and #illumos today:
https://bugs.squid-cache.org/show_bug.cgi?id=5312 and https://github.com/squid-cache/squid/pull/1551 cover core dumps from abort() when the fd limit (whether set by rlim_fd_cur, ulimit, or Squid's max_filedescriptors config setting) is less than the value of MAX_OPEN in <limits.h>.
https://bugs.squid-cache.org/show_bug.cgi?id=5314 covers core dumps in Comm::SetSelect() when called by fd_close in the exit path.