Yes, cmake creates a makefile, but I don't find any clues there. There is a file called CMakeCache.txt, which includes:
Qt Code: 
  1. Name  Value
  2. QWT  /usr/local/qwt-6.2.0/lib/libqwt.so
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which is the correct path. Anyway, don't spend more time on this problem. I will keep scratching my head though. One thing I haven't thought about before: does qmake use hard-coded paths?