Don't use GetThreadId() in wxMSW code.

Revert r73585, GetThreadId() is only available in Vista or later so don't use
it.

Just cast the handle to an integer explicitly to be able to print it with
"%x".

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73587 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775