* cygthread.cc (cygthread::async_create): Define new function.

* cygthread.h (cygthread::create): Use correct regparm.
(cygthread::standalone): Delete from class and from all constructors.
(cygthread::cygthread): Use three only arguments for detached threads, and
start the thread via QueueUserAPC/async_create.
* dcrt0.cc (dll_crt0_0): Remove handling for wincap.has_buggy_thread_startup.
(dll_crt0_1): Ditto.
* wincap.cc: Ditto throughout.
* wincap.h: Ditto.

winsup/cygwin/cygthread.cc

@@ -186,6 +186,17 @@ out:
   return info;
 }
 
+/* This function is called via QueueUserAPC.  Apparently creating threads
+   asynchronously is a huge performance win on Win64.  */
+void CALLBACK
+cygthread::async_create (ULONG_PTR arg)
+{
+  cygthread *that = (cygthread *) arg;
+  that->create ();
+  ::SetThreadPriority (that->h, THREAD_PRIORITY_HIGHEST);
+  that->zap_h ();
+}
+
 void
 cygthread::create ()
 {