FreeBSD: Testing: pthread handling

Fixing pthread usage in tsan and tsan-inout tests. pthreads are imported
as opaque pointers on FreeBDS, and thus need to be kept in an optional
pthread_t, like on Apple platforms.

Unlike on macOS, pthread_join is not annotated with nullability
annotations and thus takes an optional opaque pointer, so we don't need
to unwrap it.

Author: etcwilde

test/Sanitizers/tsan/tsan.swift

@@ -50,7 +50,7 @@ var racey_x: Int;
 
 // TSan %deflake as part of the test.
 for _ in 1...5 {
-#if os(macOS) || os(iOS)
+#if os(macOS) || os(iOS) || os(FreeBSD)
   var t : pthread_t?
 #else
   var t : pthread_t = 0
@@ -61,7 +61,7 @@ for _ in 1...5 {
 
     return nil
   }, nil)
-#if os(macOS) || os(iOS)
+#if os(macOS) || os(iOS) || os(FreeBSD)
   threads.append(t!)
 #else
   threads.append(t)

validation-test/Sanitizers/tsan-inout.swift

@@ -27,7 +27,7 @@ var gInThread2: () -> () = { }
 // Spawn two threads, run the two passed in closures simultaneously, and
 // join them.
 func testRace(name: String, thread inThread1: @escaping () -> (), thread inThread2: @escaping () -> ()) {
-#if canImport(Darwin)
+#if canImport(Darwin) || os(FreeBSD)
   var thread1: pthread_t?
   var thread2: pthread_t?
 #else