@Randomator Sir,
download the Qt Sources, e.g current the sources available are qt-everywhere-opensource-src-5.5.1, After extracting
cd C:\qt-everywhere-opensource-src-5.5.1\qtbase\src\plugins\sqldrivers\mysql
then make sure you call qmake from Qt5.5, for this purpose you can type the complete path of the qmake.
then use make and make install.
I hope it will help you.