tamer: wip-xml-xir-reader flag and setup

The original plan was to modify the existing reader to use the new
XmlXirReader, but that's going to be a lot of ongoing uncommitted work, with
both tests and implementation.  The better option seems to be to reimplement
it, since so many things are changing.

This flag will be short-lived and removed as soon as the implementation is
complete.

DEV-10863

tamer/Cargo.toml

@@ -55,3 +55,7 @@ paste = ">= 1.0.5"
 # expecting it so that it can skip those compilation steps.
 wip-frontends = []
 
+# Use the XIR-based reader for parsing xmlo files in tameld.  This flag will
+# exist only while reimplementing the XmloReader.
+wip-xmlo-xir-reader = []
+

tamer/src/obj/xmlo/reader.rs

@@ -0,0 +1,32 @@
+// XIR-based xmlo object file reader
+//
+//  Copyright (C) 2014-2021 Ryan Specialty Group, LLC.
+//
+//  This file is part of TAME.
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#[cfg(feature = "wip-xmlo-xir-reader")]
+use std::io::BufRead;
+
+#[cfg(not(feature = "wip-xmlo-xir-reader"))]
+mod quickxml;
+
+#[cfg(not(feature = "wip-xmlo-xir-reader"))]
+pub use quickxml::{XmloError, XmloEvent, XmloReader, XmloResult};
+
+#[cfg(feature = "wip-xmlo-xir-reader")]
+pub struct XmloReader<B: BufRead> {
+    todo: std::marker::PhantomData<B>,
+}