utmpx.h: add ut_host for compatibility (not posix)

Change-Id: I27e8f7b6dbc29232542e3749d8e194efa2ef5209
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3799
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

POSIX: add utmpx.h and function stubs

OpenJDK 14 assumes symbols and headers are available.

Change-Id: I21038e92afcfd2000ee95712bce874afd29611b6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3371
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>