base: Disable a warning in hdf5.cc which comes from an external header.

base: Disable a warning in hdf5.cc which comes from an external header.

This warning comes from an external header which we don't have the
ability to fix directly. We can disable it in hdf5.cc specifically
which should keep things building without defeating the warning in
cases where we could fix it.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-365

Change-Id: Ie1f4d91340e68cee7514beab9d03bba1d1c9bb38
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26325
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>