BUG #14338. Fix build issues with vtkhdf5.

vtkhdf5 is not a linkable target when using external HDF5. One must use the
module API to ensure that the linking works correctly in cases where HDF5 is
external or internal.

Change-Id: I60223a0c69a4f4748c0f7db392a11be58ec2a1f4
Merge topic '14338_fix_build_issues' into next

a4e31aa BUG #14338. Fix build issues with vtkhdf5.