When Qt is configured with d3dcompiler_qt, windeployqt should copy d3dcompiler_qt.dll along with d3dcompiler_4X (at least in debug builds).

There should also be an extra option determining if d3dcomiler_4X should be copied at all, since a release package for the Windows Store cannot have it. On Windows Phone, there isn't even a d3dcompiler_4X, so you shouldn't copy it in that case either (currently the ARM version is copied, though that's for Windows RT and won't work on the phone).