[llvm-readelf/llvm-objdump] - Improve/refactor the implementation of SHT_LLVM_ADDRSIG...

[llvm-readelf/llvm-objdump] - Improve/refactor the implementation of SHT_LLVM_ADDRSIG section dumping.

This patch:

* Adds a llvm-readobj/llvm-readelf test file for SHT_LLVM_ADDRSIG sections. (we do not have any)
* Enables dumping of SHT_LLVM_ADDRSIG with --all.
* Changes the logic to report a warning instead of an error when something goes wrong during dumping
  (allows to continue dumping SHT_LLVM_ADDRSIG and other sections on error).
* Refactors a piece of logic to a new toULEB128Array helper which might be used for GNU-style
  dumping implementation.

Differential revision: https://reviews.llvm.org/D68383

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373890 91177308-0d34-0410-b5e6-96231b3b80d8