Throughout change all calls of low_priority_sleep (0) to yield ().

* miscfuncs.cc (yield): Rename from low_priority_sleep.  Remove all of the
logic which called Sleep() and just use SwitchToThread.
* miscfuncs.h (yield): Rename from low_priority_sleep.
(SLEEP_0_STAY_LOW): Delete unused define.
* shared.cc (memory_init): Move heap_init() call directly after shared memory
initialization to more closely mimic long-standing program flow.
* tty.cc (tty_list::terminate): Replace call to low_priority_sleep with Sleep.

winsup/cygwin/sync.cc

@@ -36,7 +36,7 @@ muto::init (const char *s)
   char *already_exists = (char *) InterlockedExchangePointer (&name, s);
   if (already_exists)
     while (!bruteforce)
-      low_priority_sleep (0);
+      yield ();
   else
     {
       waiters = -1;