Disable the command pipe in ConnectionFileDescriptor for Windows.

The select() API on Windows is not compatible with objects other
than sockets, so passing a descriptor for the command pipe to this
function is guaranteed to fail.  ConnectionFileDescriptor is still
broken on Windows after this patch, but slightly less broken than
before.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@215172 91177308-0d34-0410-b5e6-96231b3b80d8