[ObjectYAML][ELF] Add support for emitting the .debug_pubnames section.

This patch helps add support for emitting the .debug_pubnames section to yaml2elf.

Known issues:
- Current implementation doesn't support emitting multiple sets of entries.
- Doesn't support DWARF64.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D82296