Support HPUX 10.20 DCE threads.
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 2f57b36..0d59ced 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -69,6 +69,12 @@
 #elif defined(__DGUX)
 #  define PY_PTHREAD_D6
 
+#elif defined(__hpux)
+/* From what I can see, HP-UX 10.20 pthreads looks
+ * like D4 flavour.
+ */
+#  define PY_PTHREAD_D4
+
 #else /* Default case */
 #  define PY_PTHREAD_STD