make lint-group-style test a UI rather than a compile-fail test

As suggested by Niko Matsakis in review
(rust-lang#38103 (comment)) regarding
the endeavor prompted by rust-lang#36846.

src/test/ui/lint/lint-group-style.rs

@@ -0,0 +1,36 @@
+// Copyright 2014–2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![deny(bad_style)]
+#![allow(dead_code)]
+
+fn CamelCase() {}
+
+#[allow(bad_style)]
+mod test {
+    fn CamelCase() {}
+
+    #[forbid(bad_style)]
+    mod bad {
+        fn CamelCase() {}
+
+        static bad: isize = 1;
+    }
+
+    mod warn {
+        #![warn(bad_style)]
+
+        fn CamelCase() {}
+
+        struct snake_case;
+    }
+}
+
+fn main() {}

src/test/ui/lint/lint-group-style.stderr

@@ -0,0 +1,67 @@
+error: function `CamelCase` should have a snake case name such as `camel_case`
+  --> $DIR/lint-group-style.rs:14:1
+   |
+14 | fn CamelCase() {}
+   | ^^^^^^^^^^^^^^^^^
+   |
+   = note: #[deny(bad_style)] implies #[deny(non_snake_case)]
+note: lint level defined here
+  --> $DIR/lint-group-style.rs:11:9
+   |
+11 | #![deny(bad_style)]
+   |         ^^^^^^^^^
+
+error: function `CamelCase` should have a snake case name such as `camel_case`
+  --> $DIR/lint-group-style.rs:22:9
+   |
+22 |         fn CamelCase() {}
+   |         ^^^^^^^^^^^^^^^^^
+   |
+   = note: #[forbid(bad_style)] implies #[forbid(non_snake_case)]
+note: lint level defined here
+  --> $DIR/lint-group-style.rs:20:14
+   |
+20 |     #[forbid(bad_style)]
+   |              ^^^^^^^^^
+
+error: static variable `bad` should have an upper case name such as `BAD`
+  --> $DIR/lint-group-style.rs:24:9
+   |
+24 |         static bad: isize = 1;
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: #[forbid(bad_style)] implies #[forbid(non_upper_case_globals)]
+note: lint level defined here
+  --> $DIR/lint-group-style.rs:20:14
+   |
+20 |     #[forbid(bad_style)]
+   |              ^^^^^^^^^
+
+warning: function `CamelCase` should have a snake case name such as `camel_case`
+  --> $DIR/lint-group-style.rs:30:9
+   |
+30 |         fn CamelCase() {}
+   |         ^^^^^^^^^^^^^^^^^
+   |
+   = note: #[warn(bad_style)] implies #[warn(non_snake_case)]
+note: lint level defined here
+  --> $DIR/lint-group-style.rs:28:17
+   |
+28 |         #![warn(bad_style)]
+   |                 ^^^^^^^^^
+
+warning: type `snake_case` should have a camel case name such as `SnakeCase`
+  --> $DIR/lint-group-style.rs:32:9
+   |
+32 |         struct snake_case;
+   |         ^^^^^^^^^^^^^^^^^^
+   |
+   = note: #[warn(bad_style)] implies #[warn(non_camel_case_types)]
+note: lint level defined here
+  --> $DIR/lint-group-style.rs:28:17
+   |
+28 |         #![warn(bad_style)]
+   |                 ^^^^^^^^^
+
+error: aborting due to 3 previous errors
+