Add support for several platforms to obtain the real thread ID.

Already had the pthread ID which is not the same.  The most obvious enhancement
is in the "core show threads" output. As stated in the utils header, if the
platform isn't supported -1 is reported (instead of the process ID previously).


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@298137 65c4cc65-6c06-0410-ace0-fbb531ad65f3