Add initial support for anyref as an opaque type (#2294)

Another round of trying to push upstream things from my fork.

This PR only adds support for anyref itself as an opaque type. It does NOT implement the full [reference types proposal](https://github.com/WebAssembly/reference-types/blob/master/proposals/reference-types/Overview.md)--so no table.get/set/grow/etc or ref.null, ref.func, etc.

Figured it was easier to review and merge as we go, especially if I did something fundamentally wrong.

***

I did put it under the `--enable-reference-types` flag as I imagine that even though this PR doesn't complete the full feature set, it probably is the right home. Lmk if not.

I'll also be adding a few github comments to places I want to point out/question.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/asmjs/asm_v_wasm.cpp b/src/asmjs/asm_v_wasm.cpp
index 32653fdba..143d6667e 100644
--- a/src/asmjs/asm_v_wasm.cpp
+++ b/src/asmjs/asm_v_wasm.cpp
@@ -53,8 +53,10 @@ AsmType wasmToAsmType(Type type) {
       return ASM_INT64;
     case v128:
       assert(false && "v128 not implemented yet");
+    case anyref:
+      assert(false && "anyref is not supported by asm2wasm");
     case exnref:
-      assert(false && "exnref is not in asm2wasm");
+      assert(false && "exnref is not supported by asm2wasm");
     case none:
       return ASM_NONE;
     case unreachable:
@@ -75,6 +77,8 @@ char getSig(Type type) {
       return 'd';
     case v128:
       return 'V';
+    case anyref:
+      return 'a';
     case exnref:
       return 'e';
     case none:
@@ -105,6 +109,8 @@ Type sigToType(char sig) {
       return f64;
     case 'V':
       return v128;
+    case 'a':
+      return anyref;
     case 'e':
       return exnref;
     case 'v':