error: 'isnan' was not declared in this scope

[antohami]

ALT Linux gcc 5.3.1, qt 5.6.2

[ 76%] Building CXX object style/CMakeFiles/adwaita-qt4.dir/adwaitamnemonics.cpp.o
In file included from /usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.cpp:20:0:
/usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.h: In static member function 'static QColor Adwaita::Helper::mix(const QColor&, const QColor&, qreal)':
/usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.h:72:27: error: 'isnan' was not declared in this scope
             if (isnan(bias)) return c1;
                           ^
/usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.h:72:27: note: suggested alternative:
In file included from /usr/include/c++/5/random:38:0,
                 from /usr/include/c++/5/bits/stl_algo.h:66,
                 from /usr/include/c++/5/algorithm:62,
                 from /usr/include/qt4/QtCore/qglobal.h:68,
                 from /usr/include/qt4/QtCore/QFlags:1,
                 from /usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaita.h:23,
                 from /usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.h:24,
                 from /usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.cpp:20:
/usr/include/c++/5/cmath:641:5: note:   'std::isnan'
     isnan(_Tp __x)
     ^
/usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.cpp: In member function 'void Adwaita::Helper::renderCheckBox(QPainter*, const QRect&, const QColor&, const QColor&, const QColor&, bool, Adwaita::CheckBoxState, qreal) const':
/usr/src/RPM/BUILD/adwaita-qt-0.97/style/adwaitahelper.cpp:835:15: warning: unused variable 'radius' [-Wunused-variable]
         qreal radius( frameRadius() );
               ^
make[2]: *** [style/CMakeFiles/adwaita-qt4.dir/adwaitahelper.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory `/usr/src/RPM/BUILD/adwaita-qt-0.97/x86_64-alt-linux-qt4/BUILD'
make[1]: *** [style/CMakeFiles/adwaita-qt4.dir/all] Error 2
make[1]: Leaving directory `/usr/src/RPM/BUILD/adwaita-qt-0.97/x86_64-alt-linux-qt4/BUILD'
make: *** [all] Error 2
make: Leaving directory `/usr/src/RPM/BUILD/adwaita-qt-0.97/x86_64-alt-linux-qt4/BUILD'
error: Bad exit status from /usr/src/tmp/rpm-tmp.38867 (%build)