Merge pull request #2553 in HDFFV/hdf5 from ~BYRN/hdf5_adb:hdf5_1_8 to hdf5_1_8
* commit '1dd7e1cd11d6acedf3e84a965784ced181e5d235':
More fixes for unused variable
Fix -Werror=unused-variable
Add -Werror= flags to lists displayed in libhdf5.settings.
Correct -Werror=unused-variable