Describe the bug
We're having trouble detecting HDF5 on some systems, in particular a cluster called rusty that is used by the Torch developers. It seems that the h5cc script is broken, and that that may be related to build system changes in HDF5. The package there is built using Nix, so it's also possible that that is doing something odd.

• Investigate HDF5 build system changes
• Create a bunch of from-source HDF5 builds with various options
• Try to detect them using the current AX_LIB_HDF5 macro
• Update or replace the macro with one that can detect all of them correctly
• Test on rusty as well, or maybe with a local Nix-built package