If you have exhausted your attempts, you can try adding the libraries manually to your linker list:
LIBS=-lvtkGUISupportQt$$_VTK_VERSION_SUFFIX \
-lvtkCommonCore$$_VTK_VERSION_SUFFIX \
-lvtkFiltersSources$$_VTK_VERSION_SUFFIX \
-lvtkRenderingCore$$_VTK_VERSION_SUFFIX \
-lvtkCommonExecutionModel$$_VTK_VERSION_SUFFIX \
-lvtkInteractionStyle$$_VTK_VERSION_SUFFIX \
-lvtkRenderingOpenGL2$$_VTK_VERSION_SUFFIX \
(...)
I do this in my project. It may be redundant, but it’s there just in case.