Issue #11006: Don't issue low level warning in subprocess when pipe2() fails.

Misc/NEWS

@@ -97,6 +97,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #11006: Don't issue low level warning in subprocess when pipe2() fails.
+
 - Issue #11829: Fix code execution holes in inspect.getattr_static for
   metaclasses with metaclasses. Patch by Andreas Stührk.
 

Modules/_posixsubprocess.c

@@ -437,12 +437,6 @@ 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