ast: Add AST::Kind::IDENTIFIER

...and return it from IdentifierExpr::get_ast_kind (). This enables
other code to dynamically test whether an expression is in fact an
IdentifierExpr.

gcc/rust/ChangeLog:
	* ast/rust-ast.h: Add AST::Kind::IDENTIFIER

Signed-off-by: Sergey Bugaev <[email protected]>

Author: bugaevc

gcc/rust/ast/rust-ast.h

@@ -44,6 +44,7 @@ enum class Kind
   UNKNOWN,
   MACRO_RULES_DEFINITION,
   MACRO_INVOCATION,
+  IDENTIFIER,
 };
 
 // Abstract base class for all AST elements
@@ -1073,6 +1074,8 @@ class IdentifierExpr : public ExprWithoutBlock
     outer_attrs = std::move (new_attrs);
   }
 
+  Kind get_ast_kind () const override { return Kind::IDENTIFIER; }
+
 protected:
   // Clone method implementation
   IdentifierExpr *clone_expr_without_block_impl () const final override