Use only unnamed pipes to launch lldb-server gdbserver.

[chaoren]

Summary

If we used unnamed pipes instead of named pipes, we can avoid having the
file system littered with debugserver-named-pipes if lldb-server happens to
crash for whatever reason. Also, on some buggy systems, it's possible to be
able to create but not to delete a fifo. Ideally, support for unnamed pipes
should be added to debugserver as well, so we can avoid the #ifdef here.

[clayborg]

This stops the fallback for Apple systems where it would try and unnamed pipe if we fail to create a named pipe. Please fix. It is ok to not try named pipes on other systems, but I would like the fallback to still work for Apple just in case.

[chaoren]

This stops the fallback for Apple systems where it would try and unnamed pipe if we fail to create a named pipe.

There's currently no support for passing unnamed pipes to debugserver (through --pipe), otherwise I would've removed the named pipes entirely.

[clayborg]

ok then, looks good as long the MacOSX test suite is happy.

lldb/trunk/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp

#endif
         Pipe port_pipe;
 
         if (host_and_port[0] && in_port == 0)
         {
             // Create a temporary file to get the stdout/stderr and redirect the
             // output of the command into this file. We will later read this file
             // if all goes well and fill the data into "command_output_ptr"
 
+#if defined(__APPLE__)
             // Binding to port zero, we need to figure out what port it ends up
             // using using a named pipe...
             error = port_pipe.CreateWithUniqueName("debugserver-named-pipe", false, named_pipe_path);
-            if (error.Success())
-            {
-                debugserver_args.AppendArgument("--named-pipe");
-                debugserver_args.AppendArgument(named_pipe_path.c_str());
-            }
-            else
+            if (error.Fail())
             {
                 if (log)
                     log->Printf("GDBRemoteCommunication::%s() "
                             "named pipe creation failed: %s",
                             __FUNCTION__, error.AsCString());
-                // let's try an unnamed pipe
-                error = port_pipe.CreateNew(true);
-                if (error.Fail())
-                {
-                    if (log)
-                        log->Printf("GDBRemoteCommunication::%s() "
-                                "unnamed pipe creation failed: %s",
-                                __FUNCTION__, error.AsCString());
-                    return error;
-                }
-                int write_fd = port_pipe.GetWriteFileDescriptor();
-                debugserver_args.AppendArgument("--pipe");
-                debugserver_args.AppendArgument(std::to_string(write_fd).c_str());
-                launch_info.AppendCloseFileAction(port_pipe.GetReadFileDescriptor());
-            }
+                return error;
+            }
+            debugserver_args.AppendArgument("--named-pipe");
+            debugserver_args.AppendArgument(named_pipe_path.c_str());
+#else
+            // Binding to port zero, we need to figure out what port it ends up
+            // using using an unnamed pipe...
+#endif
         }
         else
         {
             // No host and port given, so lets listen on our end and make the debugserver
             // connect to us..
             error = StartListenThread ("127.0.0.1", 0);
             if (error.Fail())
             {