[EH] Export tags (#4691)

This adds exported tags to `exports` section in wasm-emscripten-finalize
metadata so Emscripten can use it.

Also fixes a bug in the parser. We have only recognized the export
format of
```wasm
  (tag $e2 (param f32))
  (export "e2" (tag $e2))
```
and ignored this format:
```wasm
  (tag $e1 (export "e1") (param i32))
```

Companion patch: https://github.com/emscripten-core/emscripten/pull/17064

2 files changed, 2 insertions, 1 deletions

diff --git a/src/wasm/wasm-emscripten.cpp b/src/wasm/wasm-emscripten.cpp
index ed2f0f430..4e37464ec 100644
--- a/src/wasm/wasm-emscripten.cpp
+++ b/src/wasm/wasm-emscripten.cpp
@@ -432,7 +432,7 @@ std::string EmscriptenGlueGenerator::generateEmscriptenMetadata() {
     meta << "  \"exports\": [";
     commaFirst = true;
     for (const auto& ex : wasm.exports) {
-      if (ex->kind == ExternalKind::Function) {
+      if (ex->kind == ExternalKind::Function || ex->kind == ExternalKind::Tag) {
         meta << nextElement() << '"' << ex->name.str << '"';
       }
     }
diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index 82329af66..dd92278c6 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -3668,6 +3668,7 @@ void SExpressionWasmBuilder::parseTag(Element& s, bool preParseImport) {
     }
     ex->value = tag->name;
     ex->kind = ExternalKind::Tag;
+    wasm.addExport(ex.release());
   }
 
   // Parse typeuse