re PR debug/28063 (Dwarf no longer uses merged strings for DW_AT_comp_dir)

re PR debug/28063 (Dwarf no longer uses merged strings for DW_AT_comp_dir)

gcc/
	PR debug/28063
	* dwarf2out.c (prune_unused_types_prune): Move call to
	prune_unused_types_update_strings to cover the parent DIE also.
gcc/testuite/
	PR debug/28063
	* gcc.dg/debug/dwarf2/dwarf-merge.c: New test.
	* lib/target-supports.exp (get_compiler_messages): Add WANT_OUTPUT.
	Optionally return assembly text.  Update callers.
	(check_no_compiler_messages): Update verbose messages.
	(check_no_messages_and_pattern): New.
	(check_effective_target_string_merging): New.

From-SVN: r115874