[vtkusers] add shared library to vtk cmake project

[Liam Kurmos]

Hi All,

i hope it's ok to ask this question which is primarily a cmake question.

my cmake knowledge is fairly minimal. Now I want to link against a
external library when i build my project.

I have configured this lib in the linker with ldconfig but when i
build my project i get a linker error:
/usr/bin/ld: cannot find -ltourtre

apparently ldconfig is only for run-time linking and so i need to tell
cmake about the library.

first i tried
TARGET_LINK_LIBRARIES(testOVAS vtkWidgets vtkRendering vtkHybrid vnl tourtre)
to add libtourtre but this fails, presumably because