Compile error on QwtPolar (MinGw)

Hello,

I try to compile QwtPolar 1.1.1 for a project.

I use Qt 5.5 and Qwt 6.1.2 on Windows 8.

I get sources from here: http://qwtpolar.sourceforge.net/. After that, I use MinGw console (Qt 5.5 for Desktop) to compile the project.

No problem when doing "qmake" but when I try to compile with mingw32-make, I have an error: qwt_curve_fitter not found!

I understand it's because QwtPolar cannot found Qwt but I don't know why? QWT_ROOT is defined and add to path. I add Qwt directory into qwtpolar.pro but nothing was changed.

Can you help me, please?

Okami Ryuu