Add more posix message queue functions for Linux and all for solarish

I'm not able to run the tests locally (likely due to too old headers on Ubuntu 18.04), but I've tested my [posixmq crate](https://github.com/tormol/posixmq/tree/0decb7c82dd472024c7e90fd8121671881a81ae2) with these functions on Linux and OmniOS.