Begin work on no_std support.

This adds no_std support to a bunch of things, but more work is needed.

lib/environ/src/lib.rs

@@ -3,13 +3,9 @@
 //! the translation the base addresses of regions of memory that will hold the globals, tables and
 //! linear memories.
 
-#![deny(
-    missing_docs,
-    trivial_numeric_casts,
-    unused_extern_crates,
-    unstable_features
-)]
+#![deny(missing_docs, trivial_numeric_casts, unused_extern_crates)]
 #![warn(unused_import_braces)]
+#![cfg_attr(feature = "std", deny(unstable_features))]
 #![cfg_attr(
     feature = "clippy",
     plugin(clippy(conf_file = "../../clippy.toml"))
@@ -31,12 +27,17 @@
         use_self
     )
 )]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 extern crate cranelift_codegen;
 extern crate cranelift_entity;
 extern crate cranelift_wasm;
 #[macro_use]
 extern crate memoffset;
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc;
 
 mod compilation;
 mod environ;
@@ -46,3 +47,10 @@ mod vmcontext;
 pub use compilation::{compile_module, Compilation, Relocation, RelocationTarget, Relocations};
 pub use environ::{ModuleEnvironment, ModuleTranslation};
 pub use module::{DataInitializer, Module, TableElements};
+
+#[cfg(not(feature = "std"))]
+mod std {
+    pub use alloc::{string, vec};
+    pub use core::*;
+    pub use core::{i32, str, u32};
+}