Clang: implement requestFollowSymbol plug-in side

Invoke follow symbol in clang backend
if env variable QTC_CLANG_FOLLOW_SYMBOL is 1.
Does not include backend implementation.

Change-Id: Ia20a677830ebdd7f24800af5c5d6e8b1bf579205
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cppsymbolinfo.h

@@ -0,0 +1,45 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "cpptools_global.h"
+
+#include <QString>
+
+namespace CppTools {
+
+class CPPTOOLS_EXPORT SymbolInfo
+{
+public:
+    int startLine = 0;
+    int startColumn = 0;
+    int endLine = 0;
+    int endColumn = 0;
+    QString fileName;
+    bool failedToFollow = false;
+};
+
+} // namespace CppTools