Add 'compiler/rustc_smir/' from commit '9abcb5c7b5'

git-subtree-dir: compiler/rustc_smir
git-subtree-mainline: fb1976011e
git-subtree-split: 9abcb5c7b5

compiler/rustc_smir/src/lib.rs

@@ -0,0 +1,18 @@
+//! The WIP stable interface to rustc internals.
+//!
+//! For more information see https://github.com/rust-lang/project-stable-mir
+//!
+//! # Note
+//!
+//! This API is still completely unstable and subject to change.
+
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
+    test(attr(allow(unused_variables), deny(warnings)))
+)]
+
+#![cfg_attr(not(feature = "default"), feature(rustc_private))]
+
+pub mod mir;
+
+pub mod very_unstable;