Add a compile command to Wasmtime.

This commit adds a `compile` command to the Wasmtime CLI.

The command can be used to Ahead-Of-Time (AOT) compile WebAssembly modules.

With the `all-arch` feature enabled, AOT compilation can be performed for
non-native architectures (i.e. cross-compilation).

The `Module::compile` method has been added to perform AOT compilation.

A few of the CLI flags relating to "on by default" Wasm features have been
changed to be "--disable-XYZ" flags.

A simple example of using the `wasmtime compile` command:

```text
$ wasmtime compile input.wasm
$ wasmtime input.cwasm
```

src/commands/wasm2obj.rs

@@ -1,13 +1,12 @@
 //! The module that implements the `wasmtime wasm2obj` command.
 
 use crate::obj::compile_to_obj;
-use crate::{init_file_per_thread_logger, pick_compilation_strategy, CommonOptions};
-use anyhow::{anyhow, Context as _, Result};
+use crate::{init_file_per_thread_logger, parse_target, pick_compilation_strategy, CommonOptions};
+use anyhow::{Context as _, Result};
 use std::{
     fs::File,
     io::Write,
     path::{Path, PathBuf},
-    str::FromStr,
 };
 use structopt::{clap::AppSettings, StructOpt};
 use target_lexicon::Triple;
@@ -16,10 +15,6 @@ use target_lexicon::Triple;
 pub const WASM2OBJ_AFTER_HELP: &str = "The translation is dependent on the environment chosen.\n\
      The default is a dummy environment that produces placeholder values.";
 
-fn parse_target(s: &str) -> Result<Triple> {
-    Triple::from_str(&s).map_err(|e| anyhow!(e))
-}
-
 /// Translates a WebAssembly module to native object file
 #[derive(StructOpt)]
 #[structopt(
@@ -47,16 +42,14 @@ pub struct WasmToObjCommand {
 
 impl WasmToObjCommand {
     /// Executes the command.
-    pub fn execute(&self) -> Result<()> {
-        self.handle_module()
-    }
-
-    fn handle_module(&self) -> Result<()> {
-        if self.common.log_to_files {
-            let prefix = "wasm2obj.dbg.";
-            init_file_per_thread_logger(prefix);
-        } else {
-            pretty_env_logger::init();
+    pub fn execute(self) -> Result<()> {
+        if !self.common.disable_logging {
+            if self.common.log_to_files {
+                let prefix = "wasm2obj.dbg.";
+                init_file_per_thread_logger(prefix);
+            } else {
+                pretty_env_logger::init();
+            }
         }
 
         let strategy = pick_compilation_strategy(self.common.cranelift, self.common.lightbeam)?;