Fix a mod_ssl build problem on OS/390.

Fix a mod_ssl build problem on OS/390.

This is admittedly rather ugly code to come up with a unique 4-byte
identifier for the thread.  Since our threads are pthreads and a pthread
maps 1:1 to a TCB, the address of the TCB is sufficient.   Yes, every
TCB sees a different piece of real storage mapped to the first page,
so the code does make sense.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/ssl@95016 13f79535-47bb-0310-9956-ffa450edef68