move c++11 test into qcompilerdetection.h and make it stricter

it positively makes no sense to have a configure test which will be
never reached due to the configure/qmake bootstrap failing with a
slew of totally unhelpful error messages.

pre-standardization partial c++11 implementations are now rejected,
except for VS2013, which is still sufficient despite not announcing full
compatibility.

Change-Id: I58af10e03960af06b80cedac105cf8433f7a1745
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

config.tests/common/c++11/c++11.cpp

@@ -1,49 +0,0 @@
-/****************************************************************************
-**
-** 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 || defined(__GXX_EXPERIMENTAL_CXX0X__) || defined(__INTEL_CXX11_MODE__)
-// Compiler claims to support C++11, trust it
-#else
-#  error "__cplusplus must be >= 201103L, or one of __GXX_EXPERIMENTAL_CXX0X__ or __INTEL_CXX11_MODE__ must be defined"
-#endif
-
-#include <utility>
-#include <initializer_list>
-
-int main(int, char **) { return std::move(0); }

config.tests/common/c++11/c++11.pro

@@ -1,3 +0,0 @@
-SOURCES = c++11.cpp
-CONFIG += c++11 console
-CONFIG -= qt

configure

@@ -4430,11 +4430,7 @@ fi
 
 # Detect C++11 & up support
 stdcxx_error=false
-if ! compileTest common/c++11 "C++11"; then
+if [ "$CFG_STDCXX" = "c++11" ]; then
-    echo "ERROR: Qt requires a C++11 compiler and yours does not seem to be that."
-    echo "Please upgrade."
-    exit 1
-elif [ "$CFG_STDCXX" = "c++11" ]; then
     : # CFG_STDCXX is correct
 elif ! compileTest common/c++14 "C++14"; then
     if [ "$CFG_STDCXX" != "auto" ]; then

src/corelib/global/qcompilerdetection.h

@@ -557,6 +557,12 @@
  *  Q_COMPILER_RESTRICTED_VLA       variable-length arrays, prior to __cpp_runtime_arrays
  */
 
+#ifdef __cplusplus
+#  if __cplusplus < 201103L && !(defined(Q_CC_MSVC) && Q_CC_MSVC >= 1800)
+#    error Qt requires a C++11 compiler and yours does not seem to be that.
+#  endif
+#endif
+
 #ifdef Q_CC_INTEL
 #  define Q_COMPILER_RESTRICTED_VLA
 #  define Q_COMPILER_VARIADIC_MACROS // C++11 feature supported as an extension in other modes, too

tools/configure/configureapp.cpp

@@ -2310,12 +2310,7 @@ void Configure::autoDetection()
     detectArch();
 
     if (dictionary["C++STD"] == "auto" && !dictionary["QMAKESPEC"].contains("msvc")) {
-        if (!tryCompileProject("common/c++11")) {
+        if (!tryCompileProject("common/c++14")) {
-            dictionary["DONE"] = "error";
-            cout << "ERROR: Qt requires a C++11 compiler and yours does not seem to be that." << endl
-                 << "Please upgrade." << endl;
-            return;
-        } else if (!tryCompileProject("common/c++14")) {
             dictionary["C++STD"] = "c++11";
         } else if (!tryCompileProject("common/c++1z")) {
             dictionary["C++STD"] = "c++14";