Support exports of globals in assembler

asm.js

@@ -888,6 +888,7 @@ const Section = Object.freeze({
 const Kind = Object.freeze({
     FUNC:   0x00,
     MEM:    0x02,
+    GLOBAL: 0x03,
 });
 
 export class Assembler {
@@ -942,8 +943,28 @@ export class Assembler {
     }
 
     action_export(action) {
-        const index = Object.keys(this.funcs).indexOf(action.name);
+        const func_index = Object.keys(this.funcs).indexOf(action.name);
-        this.exports[action.name] = { kind: Kind.FUNC, index };
+        if (func_index != -1) {
+            this.exports[action.name] = {
+                kind: Kind.FUNC,
+                index: func_index,
+            };
+            return;
+        }
+
+        const global_index = Object.keys(this.globals).indexOf(action.name);
+        if (global_index != -1) {
+            this.exports[action.name] = {
+                kind: Kind.GLOBAL,
+                index: global_index,
+            };
+            return;
+        }
+
+        console.error(
+            `ERROR: Unable to resolve export ${action.name} `
+                + "(only functions and globals currently supported)"
+        );
     }
 
     action_func(action) {