Add support to link against a preinstalled nanovdb.
Add support to link against a preinstalled nanovdb.

Signed-off-by: Andre Pradhana <825a1bc3df256148afa0e85b15649bcb998dccc3@gmail.com>

dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb