stdlib: remove pthread_attr_t from _stdlib_pthread_create_block

The attributes were not being used currently.  Since this is a private
interface, remove the parameter as it makes it easier to port to
Windows.

stdlib/private/StdlibUnittest/RaceTest.swift

@@ -605,24 +605,21 @@ public func runRaceTest<RT : RaceTestWithPerTrialData>(
 
   // Create the master thread.
   do {
-    let (ret, tid) = _stdlib_pthread_create_block(
-      nil, masterThreadBody, ())
+    let (ret, tid) = _stdlib_pthread_create_block(masterThreadBody, ())
     expectEqual(0, ret)
     testTids.append(tid!)
   }
 
   // Create racing threads.
   for i in 0..<racingThreadCount {
-    let (ret, tid) = _stdlib_pthread_create_block(
-      nil, racingThreadBody, i)
+    let (ret, tid) = _stdlib_pthread_create_block(racingThreadBody, i)
     expectEqual(0, ret)
     testTids.append(tid!)
   }
 
   // Create the alarm thread that enforces the timeout.
   do {
-    let (ret, tid) = _stdlib_pthread_create_block(
-      nil, alarmThreadBody, ())
+    let (ret, tid) = _stdlib_pthread_create_block(alarmThreadBody, ())
     expectEqual(0, ret)
     alarmTid = tid!
   }

stdlib/private/SwiftPrivateThreadExtras/SwiftPrivateThreadExtras.swift

@@ -59,15 +59,8 @@ internal func invokeBlockContext(
   return context.run()
 }
 
-#if os(Cygwin) || os(FreeBSD) || os(Haiku)
-public typealias _stdlib_pthread_attr_t = UnsafePointer<pthread_attr_t?>
-#else
-public typealias _stdlib_pthread_attr_t = UnsafePointer<pthread_attr_t>
-#endif
-
 /// Block-based wrapper for `pthread_create`.
 public func _stdlib_pthread_create_block<Argument, Result>(
-  _ attr: _stdlib_pthread_attr_t?,
   _ start_routine: @escaping (Argument) -> Result,
   _ arg: Argument
 ) -> (CInt, pthread_t?) {
@@ -77,7 +70,7 @@ public func _stdlib_pthread_create_block<Argument, Result>(
   let contextAsVoidPointer = Unmanaged.passRetained(context).toOpaque()
 
   var threadID = _make_pthread_t()
-  let result = pthread_create(&threadID, attr,
+  let result = pthread_create(&threadID, nil,
     { invokeBlockContext($0) }, contextAsVoidPointer)
   if result == 0 {
     return (result, threadID)

test/Interpreter/enforce_exclusive_access.swift

@@ -120,7 +120,7 @@ ExclusiveAccessTestSuite.test("ClosureCaptureReadRead") {
 // have overlapping accesses
 ExclusiveAccessTestSuite.test("PerThreadEnforcement") {
   modifyAndPerform(&globalX) {
-    let (_, otherThread) = _stdlib_pthread_create_block(nil, { (_ : Void) -> () in
+    let (_, otherThread) = _stdlib_pthread_create_block({ (_ : Void) -> () in
       globalX.i = 12 // no-trap
       return ()
     }, ())

validation-test/stdlib/StringSlicesConcurrentAppend.swift

@@ -94,9 +94,9 @@ StringTestSuite.test("SliceConcurrentAppend") {
   expectEqual(0, ret)
 
   let (createRet1, tid1) = _stdlib_pthread_create_block(
-    nil, sliceConcurrentAppendThread, .Primary)
+    sliceConcurrentAppendThread, .Primary)
   let (createRet2, tid2) = _stdlib_pthread_create_block(
-    nil, sliceConcurrentAppendThread, .Secondary)
+    sliceConcurrentAppendThread, .Secondary)
 
   expectEqual(0, createRet1)
   expectEqual(0, createRet2)