Recommit "[DWARF5][DebugInfo]: Added support for DebugInfo generation for auto return...

Recommit "[DWARF5][DebugInfo]: Added support for DebugInfo generation for auto return type for C++ member functions."

Summary:
This was reverted in 328e0f3dcac52171b8cdedeaba22c98e7fbb75ea due to
chromium bot failure. This revision addresses that case.

Original commit message:
Summary:
    This patch will provide support for auto return type for the C++ member
    functions. Before this return type of the member function is deduced and
    stored in the DIE.
    This patch includes llvm side implementation of this feature.

    Patch by: Awanish Pandey <Awanish.Pandey@amd.com>

    Reviewers: dblaikie, aprantl, shafik, alok, SouraVX, jini.susan.george

    Reviewed by: dblaikie

    Differential Revision: https://reviews.llvm.org/D70524