[DebugInfo] Support for debug_macinfo.dwo section in llvm and llvm-dwarfdump.

This patch adds support for debug_macinfo.dwo section[pre-standardized]
to llvm and llvm-dwarfdump.

Reviewers: probinson, dblaikie, aprantl, jini.susan.george, alok

Differential Revision: https://reviews.llvm.org/D70705

Tags: #debug-info #llvm