Initial reorg.

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

crates/environ/tests/cache_disabled.rs

@@ -0,0 +1,7 @@
+use wasmtime_environ::cache_init;
+
+#[test]
+fn test_cache_disabled() {
+    let errors = cache_init::<&str>(false, None, None);
+    assert!(errors.is_empty(), "Failed to disable cache system");
+}