Clarify what versions of Windows are supported, and add Linux

specifically.

Doc/lib/libthread.tex

@@ -15,7 +15,7 @@ semaphores}) are provided.
 \index{binary semaphores}
 \index{semaphores, binary}
 
-The module is optional.  It is supported on Windows NT and '95, SGI
+The module is optional.  It is supported on Windows, Linux, SGI
 IRIX, Solaris 2.x, as well as on systems that have a \POSIX{} thread
 (a.k.a. ``pthread'') implementation.
 \index{pthreads}