do not lower-case input file names

The idc tool modified the case of its DLL or EXE input,
causing it to be all lowercase.

Task-number: QTBUG-2870
Change-Id: Ic3c028a2696786fc5b11a4018bd3fc28e362935b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>