cranelift-wasm: support multi-value Wasm (#1049)

This commit introduces initial support for multi-value Wasm. Wasm blocks and
calls can now take and return an arbitrary number of values.

The encoding for multi-value blocks means that we need to keep the contents of
the "Types" section around when translating function bodies. To do this, we
introduce a `WasmTypesMap` type that maps the type indices to their parameters
and returns, construct it when parsing the "Types" section, and shepherd it
through a bunch of functions and methods when translating function bodies.

cranelift/src/clif-util.rs

@@ -113,6 +113,12 @@ fn add_enable_simd_flag<'a>() -> clap::Arg<'a, 'a> {
         .help("Enable WASM's SIMD operations")
 }
 
+fn add_enable_multi_value<'a>() -> clap::Arg<'a, 'a> {
+    Arg::with_name("enable-multi-value")
+        .long("enable-multi-value")
+        .help("Enable WASM's multi-value support")
+}
+
 /// Returns a vector of clap value options and changes these options into a vector of strings
 fn get_vec(argument_vec: Option<clap::Values>) -> Vec<String> {
     let mut ret_vec: Vec<String> = Vec::new();
@@ -144,6 +150,7 @@ fn add_wasm_or_compile<'a>(cmd: &str) -> clap::App<'a, 'a> {
         .arg(add_input_file_arg())
         .arg(add_debug_flag())
         .arg(add_enable_simd_flag())
+        .arg(add_enable_multi_value())
 }
 
 fn handle_debug_flag(debug: bool) {
@@ -304,6 +311,7 @@ fn main() {
                     rest_cmd.is_present("time-passes"),
                     rest_cmd.is_present("value-ranges"),
                     rest_cmd.is_present("enable-simd"),
+                    rest_cmd.is_present("enable-multi-value"),
                 )
             };