[Metadata] Add GNU extensions for call site DWARF symbols

[Metadata] Add GNU extensions for call site DWARF symbols

As discussed on RFC
(http://lists.llvm.org/pipermail/llvm-dev/2019-February/130094.html), this
is set of patches that introduces debug information about call site and
call site parameters. Since the LLVM has portion of this support (dumping
DWARF 5 symbols for calls), we generate GNU extensions as well. All of that
will be restricted under an option.

([1/13] Introduce the debug entry values.)

Co-authored-by: Ananth Sowda <asowda@cisco.com>
Co-authored-by: Nikola Prica <nikola.prica@rt-rk.com>
Co-authored-by: Ivan Baev <ibaev@cisco.com>
Differential Revision: https://reviews.llvm.org/D60712

llvm-svn: 364385