The check to determine the version of VTK-m from git was duplicated in
CMakeLists.txt. Although pointless, it generally was not a big deal
(only an extra check when running CMake). Except for some reason with
the latest changes to the CMake build the second time find_package(Git)
was called on my system the GIT_EXECUTABLE variable got cleared out and
that caused the configure to fail. I have no idea why this happens (and
running CMake again seems to fix the problem), but simply removing the
extraneous find seems fix the problem.