[llvm-objdump] - Print relocation record in a GNU format.

This fixes the https://bugs.llvm.org/show_bug.cgi?id=41355.

Previously with -r we printed relocation section name instead of the target section name.
It was like this: "RELOCATION RECORDS FOR [.rel.text]"
Now it is: "RELOCATION RECORDS FOR [.text]"

Also when relocation target section has more than one relocation section,
we did not combine the output. Now we do.

Differential revision: https://reviews.llvm.org/D61312

llvm-svn: 360143