Add a CLIF interpreter

This is an incomplete version of a Cranelift IR interpreter: only a small subset of instructions are implemented and (known) missing parts are marked with TODO or FIXME.

cranelift/interpreter/src/lib.rs

@@ -0,0 +1,7 @@
+//! Cranelift IR interpreter.
+//!
+//! This module is a project for interpreting Cranelift IR.
+
+pub mod environment;
+pub mod frame;
+pub mod interpreter;