RR(S): JDK-8022616 u4 should not be used as a type for thread_id

[Dmitry Samersoff]

Please review changes:

http://cr.openjdk.java.net/~dsamersoff/JDK-8022616/webrev.02/

Story:

Tracing framework expect u4 as an id of thread

pthread_t chosen as a tread id for variety of BSD platforms couldn't be
converted to u4 so it cause compilation failure on BSD x64

Solution:

Change thread_id to pid_t and get this id  directly from kernel, the
same manner as Linux code does. Mac Os X still uses mach_port instead of
thread id.

Tested on FreeBSD and OpenBSD and also code passed jprt.

-Dmitry

-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.