Fix ITK targets within find_package()

GenerateCLP was failing to build with JsonCpp and ParameterSerializer using a static ITK.

Scanning dependencies of target GenerateCLP
[ 92%] Building CXX object GenerateCLP/CMakeFiles/GenerateCLP.dir/GenerateCLP.cxx.o
Linking CXX executable bin/GenerateCLP
/usr/bin/ld: cannot find -litkNetlibSlatec
/usr/bin/ld: cannot find -lITKStatistics
/usr/bin/ld: cannot find -lITKMesh
/usr/bin/ld: cannot find -litkzlib
/usr/bin/ld: cannot find -lITKMetaIO
/usr/bin/ld: cannot find -lITKSpatialObjects
...
Merge pull request #3 from finetjul/patch-1

Fix ITK targets within find_package()