qt5-static: Added Thiago's lto patch (1bd27f)

.. but don't use it for now (the configure script work isn't
done). Instead LTO can be attempted via QMAKE_CFLAGS and
QMAKE_LFLAGS by setting _ltcg="yes". This is also disabled
for now as it doesn't work.

adipose's lto investigations can be found at:
https://github.com/Alexpux/MINGW-packages/issues/186