Move hardlink handling out of dwz function

Move hardlink handling out of dwz function

Currently hardlink handling is done in the dwz function, on per-file basis,
with the analysis having a scope of previously processed files.

Move hardlink handling out of dwz into dedicated functions detect_hardlinks
and update_hardlinks, both called from dwz_files_1.

The detect_hardlinks is called before any file is processed, the
update_hardlinks is called after all files are processed.

This allows parallelization of the processing of the files.

2021-03-23  Tom de Vries  <tdevries@suse.de>

	* dwz.c (struct file_result): Add comment about res == -3 as
	uninitialized.  Add hardlink_to field.
	(detect_hardlinks, update_hardlinks): New function, factored out of ...
	(dwz): ... here.  Drop resa and files parameters.
	(dwz_with_low_mem): Drop resa and files parameters.
	(dwz_one_file): Update call to dwz_with_low_mem.
	(dwz_files_1): Update call to dwz_with_low_mem.  Add calls to
	detect_hardlinks and update_hardlinks.