[LLD] Report errors occurred while parsing debug info as warnings.

Summary:
Extracted from D74773. Currently, errors happened while parsing
debug info are reported as errors. DebugInfoDWARF library treats such
errors as "Recoverable errors". This patch makes debug info errors
to be reported as warnings, to support DebugInfoDWARF approach.

Reviewers: ruiu, grimar, MaskRay, jhenderson, espindola

Reviewed By: MaskRay, jhenderson

Subscribers: emaste, aprantl, arichardson, arphaman, llvm-commits

Tags: #llvm, #debug-info, #lld

Differential Revision: https://reviews.llvm.org/D75234