Patch #805613: Fix usage of the PTH library.
diff --git a/Python/thread.c b/Python/thread.c
index 87230e0..2298b38 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -98,6 +98,7 @@
 
 #ifdef HAVE_PTH
 #include "thread_pth.h"
+#undef _POSIX_THREADS
 #endif
 
 #ifdef _POSIX_THREADS