[llvm-readelf/llvm-readobj] - Check version of SHT_GNU_verdef section entries when dumping.

Elfxx_Verdef contains the following field:

vd_version
Version revision. This field shall be set to 1.
(https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html)

Our code should check the struct version for correctness. This patch does that.
(This will help to simplify or eliminate ELFDumper<ELFT>::LoadVersionDefs() which
has it's own logic to parse version definitions for no reason. It checks the
struct version currently).

Differential revision: https://reviews.llvm.org/D70810