This file must be in qt-4.x-dev.tcz :
usr/local/mkspecs/common/posix/qplatformdefs.h
it is required by usr/local/mkspecs/linux-g++/qplatformdefs.h
it includes usr/local/mkspecs/common/c89/qplatformdefs.h which is also missing
so these files are required by linux-g++/qplatformdefs.h :
usr/local/mkspecs/common/posix/qplatformdefs.h
usr/local/mkspecs/common/c89/qplatformdefs.h