Doc: change 'Posix' for 'POSIX' (GH-20001)

(cherry picked from commit 6546056)

Co-authored-by: Mathieu Dupuy <mathieu.dupuy@doctolib.com>

Author: miss-islington

Doc/howto/sockets.rst

@@ -319,7 +319,7 @@ inside-out.
 
 In Python, you use ``socket.setblocking(0)`` to make it non-blocking. In C, it's
 more complex, (for one thing, you'll need to choose between the BSD flavor
-``O_NONBLOCK`` and the almost indistinguishable Posix flavor ``O_NDELAY``, which
+``O_NONBLOCK`` and the almost indistinguishable POSIX flavor ``O_NDELAY``, which
 is completely different from ``TCP_NODELAY``), but it's the exact same idea. You
 do this after creating the socket, but before using it. (Actually, if you're
 nuts, you can switch back and forth.)

Doc/library/subprocess.rst

@@ -755,14 +755,14 @@ Instances of the :class:`Popen` class have the following methods:
 
 .. method:: Popen.terminate()
 
-   Stop the child. On Posix OSs the method sends SIGTERM to the
+   Stop the child. On POSIX OSs the method sends SIGTERM to the
    child. On Windows the Win32 API function :c:func:`TerminateProcess` is called
    to stop the child.
 
 
 .. method:: Popen.kill()
 
-   Kills the child. On Posix OSs the function sends SIGKILL to the child.
+   Kills the child. On POSIX OSs the function sends SIGKILL to the child.
    On Windows :meth:`kill` is an alias for :meth:`terminate`.
 
 

Doc/library/sysconfig.rst

@@ -74,12 +74,12 @@ places.
 
 Python currently supports seven schemes:
 
-- *posix_prefix*: scheme for Posix platforms like Linux or Mac OS X.  This is
+- *posix_prefix*: scheme for POSIX platforms like Linux or Mac OS X.  This is
   the default scheme used when Python or a component is installed.
-- *posix_home*: scheme for Posix platforms used when a *home* option is used
+- *posix_home*: scheme for POSIX platforms used when a *home* option is used
   upon installation.  This scheme is used when a component is installed through
   Distutils with a specific home prefix.
-- *posix_user*: scheme for Posix platforms used when a component is installed
+- *posix_user*: scheme for POSIX platforms used when a component is installed
   through Distutils and the *user* option is used.  This scheme defines paths
   located under the user home directory.
 - *nt*: scheme for NT platforms like Windows.