Move all trampoline compilation to wasmtime-cranelift (#3176)

* Move all trampoline compilation to `wasmtime-cranelift`

This commit moves compilation of all the trampolines used in wasmtime
behind the `Compiler` trait object to live in `wasmtime-cranelift`. The
long-term goal of this is to enable depending on cranelift *only* from
the `wasmtime-cranelift` crate, so by moving these dependencies we
should make that a little more flexible.

* Fix windows build

cranelift/wasm/src/func_translator.rs

@@ -35,6 +35,12 @@ impl FuncTranslator {
         }
     }
 
+    /// Returns the underlying `FunctionBuilderContext` that this translator
+    /// uses.
+    pub fn context(&mut self) -> &mut FunctionBuilderContext {
+        &mut self.func_ctx
+    }
+
     /// Translate a binary WebAssembly function.
     ///
     /// The `code` slice contains the binary WebAssembly *function code* as it appears in the code