Write the last part of the packet synchronously on Mono.

If we use WriteAsync and don't await it, then subsequent WriteAsync may be called before the first continuation returns. If both calls share the same buffer and they overlap, we will overwrite the data in the buffer and cause junk to arrive at receiver.

src/Build/BackEnd/Components/Communications/NodeProviderOutOfProcBase.cs

@@ -771,7 +771,7 @@ public void SendData(INodePacket packet)
 #if FEATURE_APM
                             _serverToClientStream.BeginWrite(writeStreamBuffer, i, lengthToWrite, PacketWriteComplete, null);
 #else
-                            _serverToClientStream.WriteAsync(writeStreamBuffer, i, lengthToWrite);
+                            _serverToClientStream.Write(writeStreamBuffer, i, lengthToWrite);
 #endif
                             return;
                         }