C++11: Parse alias declarations.

The parser no longer fails declarations like:
using Foo = std::vector<int>::iterator;

Change-Id: Ib3a552ebbe0147fa138db6448a52cdba8f9b9207
Reviewed-by: hjk <qthjk@ovi.com>

src/libs/3rdparty/cplusplus/ASTfwd.h

@@ -32,6 +32,7 @@ class ASTVisitor;
 class ASTMatcher;
 
 class AccessDeclarationAST;
+class AliasDeclarationAST;
 class AlignofExpressionAST;
 class ArrayAccessAST;
 class ArrayDeclaratorAST;