Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/environ/tests/cache_write_default_config.rs

@@ -0,0 +1,13 @@
+use tempfile;
+use wasmtime_environ::cache_create_new_config;
+
+#[test]
+fn test_cache_write_default_config() {
+    let dir = tempfile::tempdir().expect("Can't create temporary directory");
+    let config_path = dir.path().join("cache-config.toml");
+
+    let result = cache_create_new_config(Some(&config_path));
+    assert!(result.is_ok());
+    assert!(config_path.exists());
+    assert_eq!(config_path, result.unwrap());
+}