[llvm-readobj/llvm-objdump] - Improve how tool locate the dynamic table and...

[llvm-readobj/llvm-objdump] - Improve how tool locate the dynamic table and report warnings about that.

Before this patch we gave a priority to a dynamic table found
from the section header.

It was discussed (here: https://reviews.llvm.org/D67078?id=218356#inline-602082)
that probably preferring the table from PT_DYNAMIC is better,
because it is what runtime loader sees.

This patch makes the table from PT_DYNAMIC be chosen at first place if it is available.
But also it adds logic to fall back to SHT_DYNAMIC if the table from the dynamic segment is
broken or fall back to use no table if both are broken.

It adds a few more diagnostic warnings for the logic above.

Differential revision: https://reviews.llvm.org/D67547

llvm-svn: 372122