нашёл
CONFIG += crypto
теперь
Starting: C:/Qt/2009.01/mingw/bin/mingw32-make.exe -w
mingw32-make: Entering directory `C:/Qt/2009.01/qca1'
c:\Qt\2009.01\qt\bin\qmake.exe -spec ..\qt\mkspecs\win32-g++ -win32 -o Makefile qca1.pro
mingw32-make: Leaving directory `C:/Qt/2009.01/qca1'
mingw32-make: Entering directory `C:/Qt/2009.01/qca1'
C:/Qt/2009.01/mingw/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory `C:/Qt/2009.01/qca1'
g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -mthreads -Wl -Wl,-subsystem,windows -o debug\qca1.exe debug/qca1.o -L"c:\Qt\2009.01\qt\lib" -lmingw32 -lqtmaind -LC:\Qt\2009.01\qt\lib -lqcad -lQtGuid4 -lQtCored4
mingw32-make[1]: Leaving directory `C:/Qt/2009.01/qca1'
mingw32-make: Leaving directory `C:/Qt/2009.01/qca1'
c:\Qt\2009.01\mingw\bin\..\lib\gcc\mingw32\3.4.5\..\..\..\..\mingw32\bin\ld.exe: cannot find -lqcad
collect2: ld returned 1 exit status
mingw32-make[1]: *** [debug\qca1.exe] Error 1
mingw32-make: *** [debug] Error 2
Exited with code 2.
Error while building project qca1
When executing build step 'Make'
почему -lqcad а не -lqcad2
??