Really a strange problem.
When you specify -qtlibinfix, you get the following link error when it links libQtGui.so
.obj/release-shared/qprintengine_pdf.o: In function `QPdfEnginePrivate::writeCompressed(char const*, int)':
/depot/qt/qt-4.5/src/gui/painting/qprintengine_pdf.cpp:831: undefined reference to `compress'
.obj/release-shared/qprintengine_pdf.o: In function `QPdfEnginePrivate::writeCompressed(QIODevice*)':
/depot/qt/qt-4.5/src/gui/painting/qprintengine_pdf.cpp:761: undefined reference to `deflateInit_'
/depot/qt/qt-4.5/src/gui/painting/qprintengine_pdf.cpp:781: undefined reference to `deflate'
...

because it lacks -lz in the link command line.

this problem doesn't happen without -qtlibinfix. and doesn't happen against 4.6.0

Only test on linux. Cannot test on windows, since it fails before linking QtGui.