Add a wasmtime settings command to print Cranelift settings.

This commit adds the `wasmtime settings` command to print out available
Cranelift settings for a target (defaults to the host).

The compile command has been updated to remove the Cranelift ISA options in
favor of encouraging users to use `wasmtime settings` to discover what settings
are available.  This will reduce the maintenance cost for syncing the compile
command with Cranelift ISA flags.

crates/environ/src/data_structures.rs

@@ -11,7 +11,7 @@ pub mod ir {
 
 pub mod settings {
     pub use cranelift_codegen::settings::{
-        builder, Builder, Configurable, Flags, OptLevel, SetError,
+        builder, Builder, Configurable, Flags, OptLevel, SetError, Setting, SettingKind,
     };
 }
 

crates/wasmtime/src/module.rs

@@ -271,6 +271,15 @@ impl Module {
             return Self::deserialize(engine, &binary[COMPILED_MODULE_HEADER.len()..]);
         }
 
+        // Check to see that the config's target matches the host
+        let target = engine.config().isa_flags.triple();
+        if *target != target_lexicon::Triple::host() {
+            bail!(
+                "target '{}' specified in the configuration does not match the host",
+                target
+            );
+        }
+
         const USE_PAGED_MEM_INIT: bool = cfg!(all(feature = "uffd", target_os = "linux"));
 
         cfg_if::cfg_if! {