OK, I thought bad.

I have called the line, run qmake and qwt.prf prints the message we added earlier so that is great ! Thanks

The program compiles but it does not execute. The message "/home/developpeur/developpement/stageCamille/build-qwt_test-Desktop_Qt_5_0_2_GCC_64bit-Release/qwt_test: error while loading shared libraries: libqwt.so.6: cannot open shared object file: No such file or directory" is printed.

I have rebuild and installed qwt with qmake, to be sure it was the good one that was used but it doesn't change that.
Should I move libqwt.so.6 somewhere ? I thought that was done automatically and we should not have to care of that.