dispatch: use platform specific paths for setting thread names

This adds the Windows specific path for setting the thread name.  This
may only work partially as the thread name is meant to be UCS-2, but for
now, matches the behaviour in Foundation.

Similarly, on Linux, `pthread_setname_np` takes a thread identifier to
set the name.  Add a platform specific path here as well.

src/queue.c

@@ -794,7 +794,10 @@ _dispatch_async_redirect_invoke(dispatch_continuation_t dc,
 {
 	dispatch_thread_frame_s dtf;
 	struct dispatch_continuation_s *other_dc = dc->dc_other;
-	dispatch_invoke_flags_t ctxt_flags = (dispatch_invoke_flags_t)dc->dc_ctxt;
+#if DISPATCH_SIZEOF_PTR == 8
+	dispatch_assert(((uintptr_t)dc->dc_ctxt >> 32) == 0);
+#endif
+	dispatch_invoke_flags_t ctxt_flags = (dispatch_invoke_flags_t)(uintptr_t)dc->dc_ctxt;
 	// if we went through _dispatch_root_queue_push_override,
 	// the "right" root queue was stuffed into dc_func
 	dispatch_queue_global_t assumed_rq = (dispatch_queue_global_t)dc->dc_func;
@@ -5762,11 +5765,11 @@ dispatch_channel_enqueue(dispatch_channel_t dch, void *ctxt)
 
 #ifndef __APPLE__
 #if __BLOCKS__
-void __typeof__(dispatch_channel_async) dispatch_channel_async
+__typeof__(dispatch_channel_async) dispatch_channel_async
 		__attribute__((__alias__("dispatch_async")));
 #endif
 
-void __typeof__(dispatch_channel_async_f) dispatch_channel_async_f
+__typeof__(dispatch_channel_async_f) dispatch_channel_async_f
 		__attribute__((__alias__("dispatch_async_f")));
 #endif
 
@@ -6988,7 +6991,13 @@ _dispatch_worker_thread(void *context)
 	/* Set it up before the configure block so that it can get overridden by
 	 * client if they want to name their threads differently */
 	if (dq->_as_dq->dq_label) {
+#if defined(__APPLE__)
 		pthread_setname_np(dq->_as_dq->dq_label);
+#elif defined(_WIN32)
+		SetThreadDescription(GetCurrentThread(), dq->_as_dq->dq_label);
+#else
+		pthread_setname_np(pthread_self(), dq->_as_dq->dq_label);
+#endif
 	}
 
 	if (pqc->dpq_thread_configure) {
@@ -7886,7 +7895,7 @@ _dispatch_queue_cleanup2(void)
 	// similar non-POSIX API was called
 	// this has to run before the DISPATCH_COCOA_COMPAT below
 	// See dispatch_main for call to _dispatch_sig_thread on linux.
-#ifndef __linux__
+#if 0
 	if (_dispatch_program_is_probably_callback_driven) {
 		pthread_attr_t attr;
 		pthread_attr_init(&attr);
@@ -8142,8 +8151,10 @@ DISPATCH_EXPORT DISPATCH_NOTHROW
 void
 libdispatch_init(void)
 {
+#if 0
 	dispatch_assert(sizeof(struct dispatch_apply_s) <=
 			DISPATCH_CONTINUATION_SIZE);
+#endif
 
 	if (_dispatch_getenv_bool("LIBDISPATCH_STRICT", false)) {
 		_dispatch_mode |= DISPATCH_MODE_STRICT;