Accurately type foreign functions, and variables (attempt 2).

src/typing-asm.h

Index: src/typing-asm.h
diff --git a/src/typing-asm.h b/src/typing-asm.h
index b7f53831e6222d96d6552351d55fa7bd7e235db7..63e204e50a7cdac4cdcc128098b622845ea01754 100644
--- a/src/typing-asm.h
+++ b/src/typing-asm.h
@@ -113,6 +113,7 @@ class AsmTyper : public AstVisitor {
 
   bool in_function_;  // In module function?
   bool building_function_tables_;
+  bool visiting_exports_;
 
   TypeCache const& cache_;
 
@@ -161,6 +162,8 @@ class AsmTyper : public AstVisitor {
 
   void VisitLiteral(Literal* expr, bool is_return);
 
+  void VisitVariableProxy(VariableProxy* expr, bool assignment);
+
   void VisitIntegerBitwiseOperator(BinaryOperation* expr, Type* left_expected,
                                    Type* right_expected, Type* result_type,
                                    bool conversion);