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
```

cranelift/codegen/meta/src/gen_settings.rs

@@ -70,6 +70,72 @@ fn gen_constructor(group: &SettingGroup, parent: ParentGroup, fmt: &mut Formatte
     fmtln!(fmt, "}");
 }
 
+/// Generates the `iter_enabled` function.
+fn gen_iterator(group: &SettingGroup, fmt: &mut Formatter) {
+    fmtln!(fmt, "impl Flags {");
+    fmt.indent(|fmt| {
+        fmt.doc_comment("Iterates the enabled boolean settings.");
+        fmtln!(fmt, "pub fn iter_enabled(&self) -> impl Iterator<Item = &'static str> {");
+        fmt.indent(|fmt| {
+            fmtln!(fmt, "let mut bytes = [0; {}];", group.settings_size);
+            fmtln!(fmt, "bytes.copy_from_slice(&self.bytes[0..{}]);", group.settings_size);
+            fmtln!(fmt, "DESCRIPTORS.iter().filter_map(move |d| {");
+            fmt.indent(|fmt| {
+                fmtln!(fmt, "if match d.detail {");
+                fmt.indent(|fmt| {
+                    fmtln!(fmt, "detail::Detail::Bool { bit } => (bytes[d.offset as usize] & (1 << bit as usize)) != 0,");
+                    fmtln!(fmt, "_ => false");
+                });
+                fmtln!(fmt, "} {");
+                fmt.indent(|fmt| {
+                    fmtln!(fmt, "Some(d.name)");
+                });
+                fmtln!(fmt, "} else {");
+                fmt.indent(|fmt| {
+                    fmtln!(fmt, "None");
+                });
+                fmtln!(fmt, "}");
+            });
+            fmtln!(fmt, "})");
+        });
+        fmtln!(fmt, "}");
+    });
+    fmtln!(fmt, "}");
+}
+
+/// Generates the `is_enabled` function.
+fn gen_is_enabled(fmt: &mut Formatter) {
+    fmtln!(fmt, "impl Flags {");
+    fmt.indent(|fmt| {
+        fmt.doc_comment("Checks if a boolean setting is enabled by name.");
+        fmtln!(fmt, "pub fn is_enabled(&self, name: &str) -> bool {");
+        fmt.indent(|fmt| {
+            fmtln!(fmt, "match crate::constant_hash::probe(&TEMPLATE, name, crate::constant_hash::simple_hash(name)) {");
+            fmt.indent(|fmt| {
+                fmtln!(fmt, "Err(_) => false,");
+                fmtln!(fmt, "Ok(entry) => {");
+                fmt.indent(|fmt| {
+                    fmtln!(fmt, "let d = &TEMPLATE.descriptors[TEMPLATE.hash_table[entry] as usize];");
+                    fmtln!(fmt, "match &d.detail {");
+                    fmt.indent(|fmt| {
+                        fmtln!(fmt, "detail::Detail::Bool{ bit } => {");
+                        fmt.indent(|fmt| {
+                            fmtln!(fmt, "(self.bytes[d.offset as usize] & (1 << bit)) != 0");
+                        });
+                        fmtln!(fmt, "},");
+                        fmtln!(fmt, "_ => false");
+                    });
+                    fmtln!(fmt, "}");
+                });
+                fmtln!(fmt, "}");
+            });
+            fmtln!(fmt, "}");
+        });
+        fmtln!(fmt, "}");
+    });
+    fmtln!(fmt, "}");
+}
+
 /// Emit Display and FromStr implementations for enum settings.
 fn gen_to_and_from_str(name: &str, values: &[&'static str], fmt: &mut Formatter) {
     fmtln!(fmt, "impl fmt::Display for {} {{", name);
@@ -427,6 +493,8 @@ fn gen_group(group: &SettingGroup, parent: ParentGroup, fmt: &mut Formatter) {
     fmtln!(fmt, "}");
 
     gen_constructor(group, parent, fmt);
+    gen_iterator(group, fmt);
+    gen_is_enabled(fmt);
     gen_enum_types(group, fmt);
     gen_getters(group, fmt);
     gen_descriptors(group, fmt);