* wincap.h (wincaps::has_buggy_thread_startup): Declare.

(wincapc::has_buggy_thread_startup): Ditto.
* wincap.cc::wincap_*): Accommodate has_buggy_thread_startup.
(wincapc::init): Explicitly turn off has_buggy_thread_startup if not WOW64.
* cygthread.h (cygthread::thread_handle): Declare/define new method.
* dcrt0.cc (_dll_crt0): Don't call __sinit here.
(dll_crt0_0): Don't call sigproc_init during initialization if
wincap.has_buggy_thread_startup().
(dll_crt0_1): Defer sigproc_init to here when
wincap.has_buggy_thread_startup().  Call __sinit after we've determined that
we're not forking.
(__main): Rework comments.  Add potential future reminder.

winsup/cygwin/cygthread.h

@@ -79,6 +79,7 @@ class cygthread
   void * operator new (size_t);
   static cygthread *freerange ();
   static void terminate ();
+  HANDLE thread_handle () const {return h;}
   bool SetThreadPriority (int nPriority) {return ::SetThreadPriority (h, nPriority);}
   void zap_h ()
   {