From Kristofer Tingdahl, "the syntax of the moc executable has changed between 5.1.1 and 5.2.0 versions of qt (see below). The difference is that the <file> argument has become mandatory after the -f option.
Hence, moc will complain when osg throws in a -f without anything after it. Hence I propose removing the -f on Qt5 builds. I have tested building without -f on both qt520 and qt511, and that works well.
The attached src/osgQt/CMakeLists.txt that can be patched into 3.2 safely. For the trunk, I would consider dropping the check on the version, and simply remove the option on qt5. I have tested that on qt5.1.1, and that worked fine. Question is however if it works on qt5.0. Probably it does, so the question is simplicity of CMakeList.txt vs safety."