[stdlib] fixing compilation on Linux

Author: Max Moiseev

stdlib/private/SwiftPrivateLibcExtras/Subprocess.swift

@@ -64,7 +64,7 @@ func posixPipe() -> (readFD: CInt, writeFD: CInt) {
 /// stderr.
 public func spawnChild(args: [String])
   -> (pid: pid_t, stdinFD: CInt, stdoutFD: CInt, stderrFD: CInt) {
-  var fileActions: posix_spawn_file_actions_t = nil
+  var fileActions: posix_spawn_file_actions_t = _make_posix_spawn_file_actions_t()
   if swift_posix_spawn_file_actions_init(&fileActions) != 0 {
     preconditionFailure("swift_posix_spawn_file_actions_init() failed")
   }
@@ -140,6 +140,14 @@ public func spawnChild(args: [String])
   return (pid, childStdin.writeFD, childStdout.readFD, childStderr.readFD)
 }
 
+internal func _make_posix_spawn_file_actions_t() -> posix_spawn_file_actions_t {
+#if os(Linux) || os(FreeBSD)
+  return posix_spawn_file_actions_t()
+#else
+  return nil
+#endif
+}
+
 internal func _readAll(fd: CInt) -> String {
   var buffer = [UInt8](repeating: 0, count: 1024)
   var usedBytes = 0

stdlib/private/SwiftPrivatePthreadExtras/SwiftPrivatePthreadExtras.swift

@@ -71,7 +71,7 @@ public func _stdlib_pthread_create_block<Argument, Result>(
   let contextAsOpaque = OpaquePointer(bitPattern: Unmanaged.passRetained(context))
   let contextAsVoidPointer = UnsafeMutablePointer<Void>(contextAsOpaque)
 
-  var threadID: pthread_t = nil
+  var threadID: pthread_t = _make_pthread_t()
   let result = pthread_create(&threadID, attr,
     invokeBlockContext, contextAsVoidPointer)
   if result == 0 {
@@ -81,6 +81,14 @@ public func _stdlib_pthread_create_block<Argument, Result>(
   }
 }
 
+internal func _make_pthread_t() -> pthread_t {
+#if os(Linux) || os(FreeBSD)
+  return pthread_t()
+#else
+  return nil
+#endif
+}
+
 /// Block-based wrapper for `pthread_join`.
 public func _stdlib_pthread_join<Result>(
   thread: pthread_t,