peepmatic: Introduce the peepmatic-test crate

This crate provides testing utilities for `peepmatic`, and a test-only
instruction set we can use to check that various optimizations do or don't
apply.

cranelift/peepmatic/crates/test/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "peepmatic-test"
+version = "0.1.0"
+authors = ["Nick Fitzgerald <fitzgen@gmail.com>"]
+edition = "2018"
+publish = false
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+env_logger = "0.7.1"
+log = "0.4.8"
+peepmatic = { path = "../.." }
+peepmatic-runtime = { path = "../runtime" }