[DWARF5] Added support for emission of debug_macro section.

Summary:
This patch adds support for emission of following DWARFv5 macro forms
in .debug_macro section.

1. DW_MACRO_start_file
2. DW_MACRO_end_file
3. DW_MACRO_define_strp
4. DW_MACRO_undef_strp.

Reviewed By: dblaikie, ikudrin

Differential Revision: https://reviews.llvm.org/D72828