Auto merge of #2460 - GrayJack:haiku-utmpx, r=JohnTitor
Auto merge of #2460 - GrayJack:haiku-utmpx, r=JohnTitor

Haiku: Add utmpx functions and constants

Progressing further on #2429 adding functions and constants related to the `utmpx` structure

[Haiku headers for reference](https://github.com/haiku/haiku/blob/8f16317a5b6db5c672f331814273e5857555020f/headers/posix/utmpx.h#L13)

rust-lang/libc,rust-lang/libc,rust-lang/libc