Switch macOS to use fallback for thread ID

macOS uses a 64-bit thread ID, so rather than truncate this in
GetCurrentThreadId, use pthread_self's result and mix it with the MSBs
of the pointer to reduce the probability of a collision.

winpr/libwinpr/thread/thread.c

@@ -29,11 +29,10 @@
 
 #include <winpr/thread.h>
 
-#if defined(__MACOSX__) || defined(__FreeBSD__)
+#if defined(__FreeBSD__)
 #include <pthread_np.h>
 #elif defined(__linux__)
 #include <sys/syscall.h>
-
 #endif
 
 #ifndef MIN
@@ -918,14 +917,13 @@ HANDLE _GetCurrentThread(VOID)
 
 DWORD GetCurrentThreadId(VOID)
 {
-#if defined(__FreeBSD__) || defined(__MACOSX__)
+#if defined(__FreeBSD__)
 	int tid = pthread_getthreadid_np();
 	return tid;
 #elif defined(__linux__)
 	pid_t tid = syscall(SYS_gettid);
 	return tid;
 #else
-#warning Using possibly broken GetCurrentThreadId
 	pthread_t tid = pthread_self();
 	/* Since pthread_t can be 64-bits on some systems, take just the    */
 	/* lower 32-bits of it for the thread ID returned by this function. */