Add a test for raw identifiers

tests/target/raw_identifiers.rs

@@ -0,0 +1,50 @@
+#![feature(custom_attribute)]
+#![feature(raw_identifiers)]
+#![feature(extern_types)]
+#![allow(invalid_type_param_default)]
+#![allow(unused_attributes)]
+
+use r#foo as r#alias_foo;
+
+fn main() {
+    #[r#attr]
+    r#foo::r#bar();
+
+    let r#local = 3;
+    let r#async = r#foo(r#local);
+    r#macro!();
+
+    if let r#sub_pat @ r#Foo(_) = r#Foo(3) {}
+
+    match r#async {
+        r#Foo | r#Bar => r#foo(),
+    }
+}
+
+fn r#bar<'a, r#T>(r#x: &'a r#T) {}
+
+mod r#foo {
+    pub fn r#bar() {}
+}
+
+enum r#Foo {
+    r#Bar {},
+}
+
+trait r#Trait {
+    type r#Type;
+}
+
+impl r#Trait for r#Impl {
+    type r#Type = r#u32;
+    fn r#xxx(r#fjio: r#u32) {}
+}
+
+extern "C" {
+    type r#ccc;
+    static r#static_val: u32;
+}
+
+macro_rules! r#macro {
+    () => {};
+}