как собран qwt? и покажи .про-файл своего проекта
qwt собран как написано в INSTALL :
qmake
make && make install
.pro-файл:
TEMPLATE = app
TARGET = lab1dsp
QT += core \
gui
HEADERS += include/qwt.h \
include/qwt_abstract_scale.h \
include/qwt_abstract_scale_draw.h \
include/qwt_abstract_slider.h \
include/qwt_analog_clock.h \
include/qwt_array.h \
include/qwt_arrow_button.h \
include/qwt_clipper.h \
include/qwt_color_map.h \
include/qwt_compass.h \
include/qwt_compass_rose.h \
include/qwt_counter.h \
include/qwt_curve_fitter.h \
include/qwt_data.h \
include/qwt_dial.h \
include/qwt_dial_needle.h \
include/qwt_double_interval.h \
include/qwt_double_range.h \
include/qwt_double_rect.h \
include/qwt_dyngrid_layout.h \
include/qwt_event_pattern.h \
include/qwt_global.h \
include/qwt_interval_data.h \
include/qwt_knob.h \
include/qwt_layout_metrics.h \
include/qwt_legend.h \
include/qwt_legend_item.h \
include/qwt_legend_itemmanager.h \
include/qwt_magnifier.h \
include/qwt_math.h \
include/qwt_paint_buffer.h \
include/qwt_painter.h \
include/qwt_panner.h \
include/qwt_picker.h \
include/qwt_picker_machine.h \
include/qwt_plot.h \
include/qwt_plot_canvas.h \
include/qwt_plot_curve.h \
include/qwt_plot_dict.h \
include/qwt_plot_grid.h \
include/qwt_plot_item.h \
include/qwt_plot_layout.h \
include/qwt_plot_magnifier.h \
include/qwt_plot_marker.h \
include/qwt_plot_panner.h \
include/qwt_plot_picker.h \
include/qwt_plot_printfilter.h \
include/qwt_plot_rasteritem.h \
include/qwt_plot_scaleitem.h \
include/qwt_plot_spectrogram.h \
include/qwt_plot_zoomer.h \
include/qwt_polygon.h \
include/qwt_raster_data.h \
include/qwt_rect.h \
include/qwt_round_scale_draw.h \
include/qwt_scale_div.h \
include/qwt_scale_draw.h \
include/qwt_scale_engine.h \
include/qwt_scale_map.h \
include/qwt_scale_widget.h \
include/qwt_slider.h \
include/qwt_spline.h \
include/qwt_symbol.h \
include/qwt_text.h \
include/qwt_text_engine.h \
include/qwt_text_label.h \
include/qwt_thermo.h \
include/qwt_valuelist.h \
include/qwt_wheel.h \
lab1dsp.h
SOURCES += main.cpp \
lab1dsp.cpp
FORMS += lab1dsp.ui
RESOURCES +=
инклудники в QTDIR и QWTDIR эклипс не в упор не видит