RFR 8059533: (process) Make exiting process wait for exiting threads [win]

[Ivan Gerasimov]

Hello!

The tests that continue to fail with wrong exit codes suggest that the 
fix for JDK-8057744 wasn't sufficient.
Here's another proposal, which expands the synchronized portion of the code.
It is proposed to make the exiting process wait for the threads that 
have already started exiting.
This should help to make sure that no thread is executing any 
potentially racy code concurrently with the exiting process.

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8059533
WEBREV: http://cr.openjdk.java.net/~igerasim/8059533/0/webrev/

Comments, suggestion are welcome!

Sincerely yours,
Ivan