Backport 52502:
Fix warnings with HP's C compiler.  It doesn't recognize that infinite
loops are, um, infinite.  These conditions should not be able to happen.
diff --git a/Objects/setobject.c b/Objects/setobject.c
index 440b2fb..9d72b33 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -179,6 +179,8 @@
 		if (entry->key == dummy && freeslot == NULL)
 			freeslot = entry;
 	}
+	assert(0);	/* NOT REACHED */
+	return 0;
 }
 
 /*