Add gyp target to build preparser as stand-alone library.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 555c19ec987abe07365ae64e3ab7c41589269821..cdf456f67b6e5e2b66cdee56b3a9c19b50a3deed 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -435,6 +435,7 @@ class IterationStatement: public BreakableStatement {
   virtual IterationStatement* AsIterationStatement() { return this; }
 
   Statement* body() const { return body_; }
+  void set_body(Statement* stmt) { body_ = stmt; }
 
   // Bailout support.
   int OsrEntryId() const { return osr_entry_id_; }
@@ -531,8 +532,11 @@ class ForStatement: public IterationStatement {
   }
 
   Statement* init() const { return init_; }
+  void set_init(Statement* stmt) { init_ = stmt; }
   Expression* cond() const { return cond_; }
+  void set_cond(Expression* expr) { cond_ = expr; }
   Statement* next() const { return next_; }
+  void set_next(Statement* stmt) { next_ = stmt; }
 
   bool may_have_function_literal() const {
     return may_have_function_literal_;
@@ -744,7 +748,9 @@ class IfStatement: public Statement {
 
   Expression* condition() const { return condition_; }
   Statement* then_statement() const { return then_statement_; }
+  void set_then_statement(Statement* stmt) { then_statement_ = stmt; }
   Statement* else_statement() const { return else_statement_; }
+  void set_else_statement(Statement* stmt) { else_statement_ = stmt; }
 
  private:
   Expression* condition_;