Add infrastructure for compiletests

Also adds compilefail tests for some lints, closes #5646.

tests/compiletest/plugin/compile-fail/privatize.rs

@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![feature(plugin, custom_attribute)]
+#![plugin(plugins)]
+#![allow(dead_code)]
+
+#[privatize]
+struct Foo {
+    pub v1: i32,
+    //~^ ERROR Field v1 is public where only private fields are allowed
+    v2: i32
+}
+
+fn main() {}