Issue #12105: Add O_CLOEXEC to the os module.
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 86f587f..6ef6d9d 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1298,6 +1298,7 @@
           O_NOCTTY
           O_SHLOCK
           O_EXLOCK
+          O_CLOEXEC
 
    These constants are only available on Unix.