Bug#846996: Unable to compile with g++-6

[Thomas Viehweger <patchesThomas.Vie@web.de>]

Package: qtbase5-dev
Version: 5.7.1~20161021+dfsg-6
Severity: important

Trying to compile lxqt-panel with g++-6 and qtbase5-dev_5.7.1 results in the following errors:

In file included from /usr/include/x86_64-linux-gnu/qt5/QtCore/qlist.h:43:0,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:49,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/qplugin.h:43,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/QtPlugin:1,
                 from /home/src/lxqt-panel-de/plugin-clock/../panel/ilxqtpanelplugin.h:32,
                 from /home/src/lxqt-panel-de/plugin-clock/lxqtclock.h:34,
                 from /home/src/lxqt-panel-de/plugin-clock/lxqtclock.cpp:32:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qalgorithms.h: In function ‘uint qCountTrailingZeroBits(quint16)’:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qalgorithms.h:630:32: error: ‘__builtin_ctzs’ was not declared in this scope
     return v ? __builtin_ctzs(v) : 16U;
                                ^
/usr/include/x86_64-linux-gnu/qt5/QtCore/qalgorithms.h: In function ‘uint qCountLeadingZeroBits(quint16)’:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qalgorithms.h:693:32: error: ‘__builtin_clzs’ was not declared in this scope
     return v ? __builtin_clzs(v) : 16U;
                                ^

This is because g++ removed __builtin_clzs and __builtin_ctzs. See for example

https://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg511530.html