Revert the reversion and go with implementation described in cgf-000017, with

some modifications.
* init.cc (dll_entry): Revert previous change.
* miscfuncs.cc: Include sigproc.h for exit_thread declaration.
* winsup.h (ExitThread): Define as 'exit_thread' to ensure no accidental use.
* sigproc.cc (exit_thread): New function.
(wait_sig): Handle __SIGTHREADEXIT case.  Don't just block rather than
returning from this function.
* sigproc.h (__SIGTHREADEXIT): New enum.
(exit_thread): Declare.
* sync.cc (muto::release): Accept a tls command-line argument.
* sync.h (muto::release): Accept a tls command-line parameter.  Default to
&_my_tls.
* cygerrno.h (__set_errno): Define as extern so that no function code is ever
emitted.
* cygserver_ipc.h (cygserver_ipc.h): Ditto.
* miscfuncs.h (transform_chars): Ditto.
* path.h (has_attribute): Ditto.
* security.h (privilege_luid): Ditto.
* winsup.h (flush_file_buffers): Ditto.

winsup/cygwin/sync.h

@@ -33,7 +33,7 @@ public:
   ~muto ()
 #endif
   int acquire (DWORD ms = INFINITE) __attribute__ ((regparm (2))); /* Acquire the lock. */
-  int release () __attribute__ ((regparm (1)));		     /* Release the lock. */
+  int release (_cygtls * = &_my_tls) __attribute__ ((regparm (2))); /* Release the lock. */
 
   bool acquired () __attribute__ ((regparm (1)));
   void upforgrabs () {tls = this;}  // just set to an invalid address
@@ -60,6 +60,7 @@ public:
     if (!skip_unlock)
       locker.release ();
   }
+  static void force_release (_cygtls *tid) {locker.release (tid);}
   friend class dtable;
   friend class fhandler_fifo;
 };