Reimplement compiler default detection

Change d1b09dba45c4b3ee0f31cd9bbf6941f17afd48f0 removed the
support to detect the C++ version the compiler used by
default. In essence, it forced the compiler in C++11 mode,
if the default was still C++98.

This change reimplements the functionality in the new
configuration system.

Change-Id: Ib4bf7ade85288776f9ae2a870f19764df727e0a5
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

config.tests/common/c++98default/c++98default.cpp

@@ -0,0 +1,44 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the configuration of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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 Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** 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-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#if __cplusplus >= 201103L
+#error "compiler uses c++11 or higher by default"
+#endif
+
+int main(int, char **) {}

config.tests/common/c++98default/c++98default.pro

@@ -0,0 +1,3 @@
+TEMPLATE = app
+CONFIG -= c++11 c++14 c++1z
+SOURCES = c++98default.cpp

configure.json

@@ -238,6 +238,11 @@
             "type": "compile",
             "test": "common/c++1z"
         },
+        "cxx98default": {
+            "description": "compilers defaulting to C++98",
+            "type": "compile",
+            "test": "common/c++98default"
+        },
         "compiler": {
             "description": "Compiler",
             "type": "checkCompiler",
@@ -966,6 +971,11 @@
             "condition": "call.crossCompile",
             "output": [ "publicConfig", "privateConfig" ]
         },
+        "cxx98default": {
+            "description": "Compilers defaulting to C++98",
+            "condition": "tests.cxx98default",
+            "output": [ { "type": "publicConfig", "name": "c++11" } ]
+        },
         "compiler-flags": {
             "output": [ "compilerFlags" ],
             "priority": -3