windows-thread: New module. * lib/windows-thread.h: New file, based on lib/glthread/thread.h. * lib/windows-thread.c: New file, based on lib/glthread/thread.c. * lib/glthread/thread.h: Include windows-thread.h. (gl_thread_t): Define using glwthread_thread_t. (glthread_create): Define using glwthread_thread_create. (glthread_join): Define using glwthread_thread_join. (gl_thread_self): Define using glwthread_thread_self. (gl_thread_exit): Define using glwthread_thread_exit. (glthread_create_func, glthread_join_func, gl_thread_self_func, gl_thread_exit_func): Remove declarations. * lib/glthread/thread.c (self_key): Remove variable. (do_init_self_key, init_self_key): Remove functions. (struct gl_thread_struct): Remove type. (get_current_thread_handle, gl_thread_self_func, wrapper_func, glthread_create_func, glthread_join_func, gl_thread_exit_func): Remove functions. * modules/windows-thread: New file. * modules/thread (Depends-on): Add windows-thread.