fcntl: add F_DUPFD_CLOEXEC constant, available on Linux 2.6.24+.

Misc/NEWS

@@ -206,6 +206,8 @@ Core and Builtins
 Library
 -------
 
+- fcntl: add F_DUPFD_CLOEXEC constant, available on Linux 2.6.24+.
+
 - Issue #15972: Fix error messages when os functions expecting a file name or
   file descriptor receive the incorrect type.
 

Modules/fcntlmodule.c

@@ -461,6 +461,9 @@ all_ins(PyObject* d)
 #ifdef F_DUPFD
     if (ins(d, "F_DUPFD", (long)F_DUPFD)) return -1;
 #endif
+#ifdef F_DUPFD_CLOEXEC
+    if (ins(d, "F_DUPFD_CLOEXEC", (long)F_DUPFD_CLOEXEC)) return -1;
+#endif
 #ifdef F_GETFD
     if (ins(d, "F_GETFD", (long)F_GETFD)) return -1;
 #endif