#6416: Fix compilation of the select module on Windows, as well as test_subprocess:
PIPE_BUF is not defined on Windows, and probably has no meaning there.
Anyway the subprocess module uses another way to perform non-blocking reads (with a thread)
diff --git a/Doc/library/select.rst b/Doc/library/select.rst
index 469fbac..7ca9fde 100644
--- a/Doc/library/select.rst
+++ b/Doc/library/select.rst
@@ -105,7 +105,7 @@
Files reported as ready for writing by :func:`select`, :func:`poll` or
similar interfaces in this module are guaranteed to not block on a write
of up to :const:`PIPE_BUF` bytes.
- This value is guaranteed by POSIX to be at least 512.
+ This value is guaranteed by POSIX to be at least 512. Availability: Unix.
.. versionadded:: 2.7