Add support for reference types proposal (#2451)

This adds support for the reference type proposal. This includes support
for all reference types (`anyref`, `funcref`(=`anyfunc`), and `nullref`)
and four new instructions: `ref.null`, `ref.is_null`, `ref.func`, and
new typed `select`. This also adds subtype relationship support between
reference types.

This does not include table instructions yet. This also does not include
wasm2js support.

Fixes #2444 and fixes #2447.

1 files changed, 4 insertions, 6 deletions

diff --git a/src/support/small_vector.h b/src/support/small_vector.h
index 7f00bd4a6..d4ad961a7 100644
--- a/src/support/small_vector.h
+++ b/src/support/small_vector.h
@@ -38,17 +38,15 @@ template<typename T, size_t N> class SmallVector {
   std::vector<T> flexible;
 
 public:
+  using value_type = T;
+
   SmallVector() {}
 
   T& operator[](size_t i) {
-    if (i < N) {
-      return fixed[i];
-    } else {
-      return flexible[i - N];
-    }
+    return const_cast<T&>(static_cast<const SmallVector<T, N>&>(*this)[i]);
   }
 
-  T operator[](size_t i) const {
+  const T& operator[](size_t i) const {
     if (i < N) {
       return fixed[i];
     } else {