Support source-level debugging (e.g. by generating DWARF info)

[fwcd]

Add a flag (e.g. -g similar to contemporary C compilers) for generating source-level debug info, e.g. in the DWARF format. This should make it possible to use debuggers such as lldb or gdb to step through compiled binaries.

Some useful references:

• https://dwarfstd.org/
• https://developer.ibm.com/articles/au-dwarf-debug-format/
• https://stackoverflow.com/questions/20930801/dwarf-hello-world-assembly-example-or-tutoral

Note that NASM already seems to have some level of support for generating DWARF info that maps to the Assembly File, but since we're interested in higher-level source mapping, we will probably have to redo this ourselves in the code generator.