[dsymutil] Unify error handling outside DwarfLinker.

This is a follow-up to r327137 where we unified error handling for the
DwarfLinker. This replaces calls to errs() and outs() with the
appropriate ostream wrapper everywhere in dsymutil.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327411 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed