fail to build c3d with the master branch

[hubutui]

step to build:

git clone https://github.com/pyushkevich/c3d.git
cd c3d
cmake -B build -DBUILD_GUI=ON -DBUILD_TESTING=OFF -DCMAKE_CXX_FLAGS="-I/usr/include/eigen3" .
cd build
make

the commit I used is f7e9d5c
gcc: 11.2.0
itk: 5.2.1
eigen: 3.4.0
check the complete build log here

[carandraug]

There are two errors here:

1. redeclaration of it in ``itk::LabelImageGaussianInterpolateImageFunction.EvaluateAtContinuousIndex()(ignore it by building with-DCMAKE_CXX_FLAGS="-Wshadow")
2. some more cryptic issues about pure virtual functions which boils down to ITK5 not currently being supported (you need to build against ITK4)

I've made pull request #33 which fixes both of those issues.