Make the QT_USE_FREETYPE_LCDFILTER define be configurable in the Qt configure script

It would be nice if the QT_USE_FREETYPE_LCDFILTER define was configurable in the configure script, this define controls the usage of FT_Library_SetLcdFilter(), and this function may be problematic when distributing the Qt libraries from one system to another, it may not be present in the FreeType library of the target system(s).