Fix the debuglink following code to recursively load links found in the newly loaded...

Fix the debuglink following code to recursively load links found in the newly loaded debug info.

	PR 26595
	* dwarf.c (load_separate_debug_info): Return NULL rather than
	FALSE in error situations.
	(load_separate_debug_file): Move code to load debug links to ...
	(check_for_and_load_links): ... here.  New function.  Load
	separate debug information pointed to by debuglink and
	debugaltlink sections.  Recursively scan newly loaded debug
	information for more links and load them too.