[llvm-readobj/llvm-readelf] - Implement GNU style dumper of the SHT_GNU_verdef section.

It was not implemented yet, we had only LLVM style dumper implemented.
Section description is here: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html

Differential revision: https://reviews.llvm.org/D62520

llvm-svn: 362082