Qt pkgconfig flags should contain -fPIC

$ echo "#include <QtCore/QCoreApplication>" > foo.cc
$ g++ $(pkg-config --cflags Qt5Core) -c foo.cc
In file included from /usr/include/x86_64-linux-gnu/qt5/QtCore/qcoreapplication.h:37:0,
                 from /usr/include/x86_64-linux-gnu/qt5/QtCore/QCoreApplication:1,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/qt5/QtCore/qglobal.h:1067:4: error: #error "You must build your code with position independent code if Qt was built with -reduce-relocations. " "Compile your code with -fPIC (-fPIE is not enough)."
 #  error "You must build your code with position independent code if Qt was built with -reduce-relocations. "\
    ^