gazebo ebuild depends on sci-libs/hdf5 but its support is not effectively enabled because the -DHDF5_INSTRUMENT definition is missing. Unfortunately the source code supports only <hdf5-1.10, I am going to submit a PR on github to fix both issues
Please skip the failing tests via CMAKE_SKIP_TESTS=() in src_test, don't disable them globally.
I have changed the target of the PR, I will exclude any change on the test part because there are too many failing and it is out of my scope :-(