Oh yes, altogether 6 paths: (sorry for repetition)
export QTDIR=/usr/lib/qt
export QT_LIBRARY_PATH
export QMAKESPEC=/usr/lib/qt/mkspecs/default
export QT_PLUGINSDIR=/usr/lib/qt/plugins
export LD_LIBRARY_PATH=/usr/lib/qt/lib
export PKG_CONFIG_PATH=/opt/native/arm/3.3.2-xscale-softvfp/armv5tel-cacko-linux/lib/pkgconfig (dunno why I just need to do this every time. perhaps sth got wrong in my /etc/profile)
I repeated 3 times and have tried make clean to start over and even decompress the source to build afresh, but kept running into exactly the same make error.