bpo-39850: Add support for abstract sockets in multiprocessing (GH-18866)

diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py
index 87ebef6..215ac39 100644
--- a/Lib/multiprocessing/forkserver.py
+++ b/Lib/multiprocessing/forkserver.py
@@ -55,7 +55,8 @@
         os.waitpid(self._forkserver_pid, 0)
         self._forkserver_pid = None
 
-        os.unlink(self._forkserver_address)
+        if not util.is_abstract_socket_namespace(self._forkserver_address):
+            os.unlink(self._forkserver_address)
         self._forkserver_address = None
 
     def set_forkserver_preload(self, modules_names):
@@ -135,7 +136,8 @@
             with socket.socket(socket.AF_UNIX) as listener:
                 address = connection.arbitrary_address('AF_UNIX')
                 listener.bind(address)
-                os.chmod(address, 0o600)
+                if not util.is_abstract_socket_namespace(address):
+                    os.chmod(address, 0o600)
                 listener.listen()
 
                 # all client processes own the write end of the "alive" pipe;