Add support for io_uring

Summary: Sets out the foundation of io_uring support into fizz and enables support in the fizz tool

Reviewed By: mingtaoy

Differential Revision: D23592810

fbshipit-source-id: 6f995c99541bc2aeca3cdfb7d84ebd2d25eb1f5e

folly/io/async/test/MockAsyncTransport.h

@@ -25,6 +25,7 @@ namespace test {
 
 class MockAsyncTransport : public AsyncTransport {
  public:
+  MOCK_METHOD1(setEventCallback, void(EventRecvmsgCallback*));
   MOCK_METHOD1(setReadCB, void(ReadCallback*));
   MOCK_CONST_METHOD0(getReadCallback, ReadCallback*());
   MOCK_CONST_METHOD0(getReadCB, ReadCallback*());