Merge with 3.2 for #11006.

Misc/NEWS

@@ -419,6 +419,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #11006: Don't issue low level warning in subprocess when pipe2() fails.
+
 - Issue #13620: Support for Chrome browser in webbrowser.py Patch contributed
   by Arnaud Calmettes.
 

Modules/_posixsubprocess.c

@@ -442,12 +442,6 @@ subprocess_cloexec_pipe(PyObject *self, PyObject *noargs)
     Py_END_ALLOW_THREADS
     if (res != 0 && errno == ENOSYS)
     {
-        if (PyErr_WarnEx(
-                PyExc_RuntimeWarning,
-                "pipe2 set errno ENOSYS; falling "
-                "back to non-atomic pipe+fcntl.", 1) != 0) {
-            return NULL;
-        }
         {
 #endif
         /* We hold the GIL which offers some protection from other code calling