Replace compiletest suite by doc-tests with compile_fail

compiletest-rs use internal rustc APIs and is broken in today’s Nightly.
rustdoc however is maintained with rustc and so much less fragile.

tests/unit/deny_public_fields/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "deny_public_fields_tests"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+
+[lib]
+path = "lib.rs"
+test = false
+
+[dependencies]
+deny_public_fields = {path = "../../../components/deny_public_fields"}

tests/unit/deny_public_fields/lib.rs

@@ -0,0 +1,33 @@
+/* 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/. */
+
+/**
+```compile_fail
+#[macro_use] extern crate deny_public_fields;
+
+#[derive(DenyPublicFields)]
+struct Foo {
+    pub v1: i32,
+    v2: i32
+}
+
+fn main() {}
+```
+*/
+pub fn deny_public_fields_failing() {}
+
+/**
+```
+#[macro_use] extern crate deny_public_fields;
+
+#[derive(DenyPublicFields)]
+struct Foo {
+    v1: i32,
+    v2: i32
+}
+
+fn main() {}
+```
+*/
+pub fn deny_public_fields_ok() {}