Please read carefully: your problem is completely different.

In the first report the qwt library was found by the linker, but identified as incompatible ( obviously not cross compiled ). Your message instead tells you, that the library is not found at all.

Check the paths you pass to the linker ( -L/... ) in your makefile if a valid libqwt.so can be found. If true try a "file /.../libqwt.so", if it has been really cross compiled.

Uwe