[modules] Basic support of exports

src/ast/variables.h

Index: src/ast/variables.h
diff --git a/src/ast/variables.h b/src/ast/variables.h
index b56fb5b3483bb94bf758a41360ee148788e38ec0..6ecae7fd85d50631c235a7258cf2592a37fb689c 100644
--- a/src/ast/variables.h
+++ b/src/ast/variables.h
@@ -113,6 +113,11 @@ class Variable final : public ZoneObject {
 
   int index() const { return index_; }
 
+  bool IsExport() const {
+    DCHECK(location() == VariableLocation::MODULE);
+    return index() == 0;
+  }
+
   void AllocateTo(VariableLocation location, int index) {
     DCHECK(IsUnallocated() ||
            (this->location() == location && this->index() == index));