[llvm-readobj][test] - Add a check for --dyn-syms.

We have a `-dyn-symbols` option. It has a `--dyn-syms` alias
that is not tested in llvm-readobj tests currently.

There was a Object/readobj-elf-versioning.test where it is used,
but I've removed it in D73163. And also it is not the
right place to test it anyways.

Differential revision: https://reviews.llvm.org/D73164