[llvm-readobj] Implement --dependent-libraries for GNU output
Previously, the option was only implemented for LLVM output. This fixes
At the current time, GNU readelf does not support this option.
Consequently, this patch simply attempts to roughly follow the output
style for similar options like --syms/--notes etc, combined with
Reviewed by: MaskRay, grimar
Differential Revision: https://reviews.llvm.org/D79939