qt: fix static linking

`-ldl` option is used unconditionally in `QMAKE_LIBS_DYNLOAD` while libdl is
not supported when libc is static. As the value of `QMAKE_LIBS_DYNLOAD` goes
into 'Libs.private' field of the pkgconfig files created by qmake, static
linking with qt will fail with:
  /usr/bin/ld: cannot find -ldl

Fix this issue by adding a build test to configure to check if libdl is
supported. `QMAKE_LIBS_DYNLOAD` in "src/corelib/plugin/plugin.pri" is now used
only if libdl is available.

Fixes:
http://autobuild.buildroot.net/results/459/4596b9c69cbc387f1071c730aaac76723afaa853/
http://autobuild.buildroot.net/results/459/4596b9c69cbc387f1071c730aaac76723afaa853/

Backported from Qt5:
https://github.com/qtproject/qtbase/commit/f669ea0d54302de31456d57286aa0e4ca1443e98

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

diff --git a/package/qt/0011-Link-with-ldl-option-only-when-it-is-supported.patch b/package/qt/0011-Link-with-ldl-option-only-when-it-is-supported.patch
new file mode 100644 (file)
index 0000000..f3d47f7
--- /dev/null
+++ b/package/qt/0011-Link-with-ldl-option-only-when-it-is-supported.patch
@@ -0,0 +1,116 @@
+From 438f088ad520ac91ae47dba9a515ab0d1088c89c Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?J=C3=B6rg=20Krause?= <joerg.krause@embedded.rocks>
+Date: Fri, 15 Apr 2016 03:32:02 +0200
+Subject: [PATCH] Link with -ldl option only when it is supported
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+`-ldl` option is used unconditionally in `QMAKE_LIBS_DYNLOAD` while libdl is
+not supported when libc is static. As the value of `QMAKE_LIBS_DYNLOAD` goes
+into 'Libs.private' field of the pkgconfig files created by qmake, static
+linking with qt will fail with:
+  /usr/bin/ld: cannot find -ldl
+
+Fix this issue by adding a build test to configure to check if libdl is
+supported. `QMAKE_LIBS_DYNLOAD` in "src/corelib/plugin/plugin.pri" is now used
+only if libdl is available.
+
+Backported from Qt5:
+https://github.com/qtproject/qtbase/commit/f669ea0d54302de31456d57286aa0e4ca1443e98
+
+Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
+---
+ config.tests/unix/libdl/libdl.cpp | 39 +++++++++++++++++++++++++++++++++++++++
+ config.tests/unix/libdl/libdl.pro |  3 +++
+ configure                         |  6 ++++++
+ src/corelib/plugin/plugin.pri     |  2 +-
+ 4 files changed, 49 insertions(+), 1 deletion(-)
+ create mode 100644 config.tests/unix/libdl/libdl.cpp
+ create mode 100644 config.tests/unix/libdl/libdl.pro
+
+diff --git a/config.tests/unix/libdl/libdl.cpp b/config.tests/unix/libdl/libdl.cpp
+new file mode 100644
+index 0000000..28a8233
+--- /dev/null
++++ b/config.tests/unix/libdl/libdl.cpp
+@@ -0,0 +1,39 @@
++/****************************************************************************
++**
++** Copyright (C) 2015 The Qt Company Ltd.
++** Contact: http://www.qt.io/licensing/
++**
++** This file is part of the config.tests of the Qt Toolkit.
++**
++** $QT_BEGIN_LICENSE:LGPL21$
++** 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 2.1 or version 3 as published by the Free
++** Software Foundation and appearing in the file LICENSE.LGPLv21 and
++** LICENSE.LGPLv3 included in the packaging of this file. Please review the
++** following information to ensure the GNU Lesser General Public License
++** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
++** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
++**
++** As a special exception, The Qt Company gives you certain additional
++** rights. These rights are described in The Qt Company LGPL Exception
++** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
++**
++** $QT_END_LICENSE$
++**
++****************************************************************************/
++
++#include <dlfcn.h>
++
++int main(int, char **)
++{
++    dlopen(0, 0);
++}
+diff --git a/config.tests/unix/libdl/libdl.pro b/config.tests/unix/libdl/libdl.pro
+new file mode 100644
+index 0000000..a643934
+--- /dev/null
++++ b/config.tests/unix/libdl/libdl.pro
+@@ -0,0 +1,3 @@
++SOURCES = libdl.cpp
++CONFIG -= qt dylib
++LIBS += -ldl
+\ No newline at end of file
+diff --git a/configure b/configure
+index 10ad7ca..1c70691 100755
+--- a/configure
++++ b/configure
+@@ -5506,6 +5506,12 @@ if [ "$CFG_LIBPNG" = "auto" ]; then
+     fi
+ fi
+ 
++# detect dl
++if ! compileTest unix/libdl "libdl"; then
++    QMakeVar add DEFINES QT_NO_DYNAMIC_LIBRARY
++    QMAKE_CONFIG="$QMAKE_CONFIG no-libdl"
++fi
++
+ # detect accessibility
+ if [ "$CFG_ACCESSIBILITY" = "auto" ]; then
+     if [ "$XPLATFORM_SYMBIAN" = "yes" ]; then
+diff --git a/src/corelib/plugin/plugin.pri b/src/corelib/plugin/plugin.pri
+index eb7a7f7..c342f2e 100644
+--- a/src/corelib/plugin/plugin.pri
++++ b/src/corelib/plugin/plugin.pri
+@@ -32,4 +32,4 @@ integrity {
+       SOURCES += plugin/qlibrary_unix.cpp
+ }
+ 
+-LIBS_PRIVATE += $$QMAKE_LIBS_DYNLOAD
++!no-libdl: LIBS_PRIVATE += $$QMAKE_LIBS_DYNLOAD
+-- 
+2.8.0
+