Supports writing the first function. Still TODO is:
 * handling the .debug_line header growing too large
 * adding a new file to an existing compilation
 * adding an additional function to an existing file
 * handling incremental updates
 * adding the main IR debug ops for IR instructions

There are also issues to work out:
 * readelf --debug-dump=rawline is saying there is no .debug_str section
   even though there is
 * readelf --debug-dump=decodedline is saying the file index 0 is bad
   and reporting some other kind of corruption.