PR gold/12898

	PR gold/12898
	* layout.cc (Layout::segment_precedes): Don't crash if a linker
	script create indistinguishable segments.
	(Layout::set_segment_offsets): Use stable_sort when sorting
	segments.  Pass this to Compare_segments constructor.
	* layout.h (class Layout): Make segment_precedes non-static.
	(class Compare_segments): Change from struct to class.  Add
	layout_ field.  Add constructor.
	* script-sections.cc
	(Script_sections::attach_sections_using_phdrs_clause): Rename
	local orphan to is_orphan.  Don't report failure to put empty
	section in segment.  On attachment failure, report name of
	section, and attach to first PT_LOAD segment.