MFC	r268097:

MFV	r260708
4427 pid provider rejects probes with valid UTF-8 names

This make use of Solaris' u8_validate() which we happen to
use since r185029 for ZFS.
Use of u8_textprep.c required -Wno-cast-qual for powerpc.

Illumos Revision:	1444d846b126463eb1059a572ff114d51f7562e5

Reference:
https://www.illumos.org/issues/4427

Obtained from:	Illumos