[lldb] Support for DWARF-5 atomic types

Summary:
This patch adds support for atomic types (DW_TAG_atomic_type) to LLDB. It's mostly just filling out all the switch-statements that didn't implement Atomic case with the usual boilerplate.

Thanks Pavel for writing the test case.

Reviewers: labath, aprantl, shafik

Reviewed By: labath

Subscribers: jfb, abidh, JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D71183