Add config test for Khronos development headers

These are needed on Linux, since the core layer can
not rely on the shipped third_party/khronos headers
because that would break the build on GLES configs.

Change-Id: I598f58a9830b31a56425db60b7fc36c3f34f8581
Reviewed-by: Michael Brüning <michael.bruning@theqtcompany.com>

tools/qmake/config.tests/khr/khr.cpp

+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtWebEngine module 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 http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://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.LGPLv3 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.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 later as published by the Free
+** Software Foundation and appearing in the file LICENSE.GPL included in
+** the packaging of this file. Please review the following information to
+** ensure the GNU General Public License version 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <KHR/khrplatform.h>
+
+int main(int, char **)
+{
+    const khronos_boolean_enum_t kfalse = KHRONOS_FALSE;
+    const khronos_boolean_enum_t ktrue = KHRONOS_TRUE;
+    return kfalse == ktrue;
+}

tools/qmake/config.tests/khr/khr.pro

+CONFIG-=qt
+linux:SOURCES += khr.cpp

tools/qmake/mkspecs/features/configure.prf

@@ -20,7 +20,8 @@ defineTest(runConfigure) {
         qtCompileTest($$test)
     }
     # libcap-dev package doesn't ship .pc files on Ubuntu.
-    linux:!config_libcap:skipBuild("libcap appears to be missing")
+    linux:!config_libcap:skipBuild("libcap development package appears to be missing")
+    linux:!config_khr:skipBuild("khronos development headers appear to be missing (mesa/libegl1-mesa-dev)")
     contains(QT_CONFIG, xcb) {
         for(package, $$list("libdrm xcomposite xi xrandr")) {
             !packagesExist($$package):skipBuild("Unmet dependency: $$package")