Add 0 to _POSIX_SEMAPHORES. Will backport to 2.4.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index d754005..a415a43 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -16,7 +16,9 @@
family of functions must indicate this by defining
_POSIX_SEMAPHORES. */
#ifdef _POSIX_SEMAPHORES
-#if _POSIX_SEMAPHORES == -1
+/* On FreeBSD 4.x, _POSIX_SEMAPHORES is defined empty, so
+ we need to add 0 to make it work there as well. */
+#if (_POSIX_SEMAPHORES+0) == -1
#define HAVE_BROKEN_POSIX_SEMAPHORES
#else
#include <semaphore.h>
