From: Brian Behlendorf <behlendorf1@llnl.gov>
Subject: [PATCH] feature pthreads

This converts the userspace code to use the POSIX threads API instead of
the Solaris-only threads API.  The API is almost identical and POSIX
threads are a standard, so this is also a no-brainer and it's also
going upstream.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>