Disable flakey test on Mac.

c++/src/kj/compat/http-test.c++

@@ -2601,8 +2601,16 @@ KJ_TEST("HttpClient connection management") {
       .wait(io.waitScope).body->readAllBytes().wait(io.waitScope);
   KJ_EXPECT(count == 0);
 
-#if !_WIN32  // TODO(soon): Figure out why this doesn't work on Windows. Probably a bug in
-             //   Win32IocpEventPort::poll().
+#if __linux__
+  // TODO(soon): Figure out why this doesn't work on Windows and is flakey on Mac. My guess is that
+  //   the closing of the TCP connection propagates synchronously on Linux so that by the time we
+  //   poll() the EventPort it reports the client end of the connection has reached EOF, whereas on
+  //   Mac and Windows this propagation probably involves some concurrent process which may or may
+  //   not complete before we poll(). A solution in this case would be to use a dummy in-memory
+  //   ConnectionReceiver that returns in-memory pipes (see UnbufferedPipe earlier in this file),
+  //   so that we don't rely on any non-local behavior. Another solution would be to pause for
+  //   a short time, maybe.
+
   // If the server times out the connection, we figure it out on the client.
   doRequest().wait(io.waitScope);
   KJ_EXPECT(count == 1);