[llvm-readobj/llvm-readelf] - Report a warning instead of a error when dumping a broken dynamic section.

It does not make sence to stop dumping the object if the broken
dynamic section was found. In this patch I changed the behavior from
"report an error" to "report a warning". This matches GNU.

Differential revision: https://reviews.llvm.org/D64472

llvm-svn: 365762