RFR: CR7171422: Change 7161732 breaks SA on Windows

[Rickard Bäckman]

Hi,

my refactoring broke the SA on Windows, the only platform that didn't 
have a declaration of the thread_id type in vmStructs.

This change adds the declares the field as an unsigned integer.
Tested by building in JPRT and connecting with jsadebugd.exe on Win64.

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7171422
Webrev: http://cr.openjdk.java.net/~rbackman/7171422/webrev/

Thanks
/R