gthread-win32.c: link to html broken

[Felix Kater <fkater googlemail com>]

In gthread-win32.c, the link to

http://www2.awl.com/cseng/titles/0-201-63465-1/csmutx.htm

seems to be redirected to a bookstore. I have searched "cseng csmutx"
and found this (which was probably meant):

http://world.std.com/~jmhart/csmutx.htm

Felix