Remove usage of CompilationStrategy from Config (#764)

* Remove usage of `CompilationStrategy` from `Config`

This commit removes the public API usage of the internal
`CompilationStrategy` enumeration from the `Config` type in the
`wasmtime` crate. To do this the `enum` was copied locally into the
crate and renamed `Strategy`. The high-level description of this change
is:

* The `Config::strategy` method now takes a locally-defined `Strategy`
  enumeration instead of an internal type.

* The contents of `Strategy` are always the same, not relying on Cargo
  features to indicate which variants are present. This avoids
  unnecessary downstream `#[cfg]`.

* A `lightbeam` feature was added to the `wasmtime` crate itself to
  lightbeam compilation support.

* The `Config::strategy` method is now fallible. It returns a runtime
  error if support for the selected strategy wasn't compiled in.

* The `Strategy` enum is listed as `#[non_exhaustive]` so we can safely
  add variants over time to it.

This reduces the public crate dependencies of the `wasmtime` crate
itself, removing the need to reach into internal crates even more!

cc #708

* Fix fuzz targets

* Update nightly used to build releases

* Run rustfmt

crates/fuzzing/src/oracles.rs

@@ -32,14 +32,15 @@ fn host_isa() -> Box<dyn isa::TargetIsa> {
 /// Performs initial validation, and returns early if the Wasm is invalid.
 ///
 /// You can control which compiler is used via passing a `CompilationStrategy`.
-pub fn instantiate(wasm: &[u8], compilation_strategy: CompilationStrategy) {
+pub fn instantiate(wasm: &[u8], strategy: Strategy) {
     if wasmparser::validate(wasm, None).is_err() {
         return;
     }
 
     let mut config = Config::new();
-    config.strategy(compilation_strategy);
-
+    config
+        .strategy(strategy)
+        .expect("failed to enable lightbeam");
     let engine = Engine::new(&config);
     let store = HostRef::new(Store::new(&engine));
 

crates/fuzzing/tests/regressions.rs

@@ -5,10 +5,11 @@
 //! use the Wasm binary by including it via
 //! `include_bytes!("./regressions/some-descriptive-name.wasm")`.
 
+use wasmtime::Strategy;
 use wasmtime_fuzzing::oracles;
 
 #[test]
 fn instantiate_empty_module() {
     let data = wat::parse_str(include_str!("./regressions/empty.wat")).unwrap();
-    oracles::instantiate(&data, wasmtime_jit::CompilationStrategy::Auto);
+    oracles::instantiate(&data, Strategy::Auto);
 }