PR gold/12880

	PR gold/12880
	* layout.h (class Layout): Add interp_segment_ field.
	* layout.cc (Layout::Layout): Initialize interp_segment_ field.
	(Layout::attach_allocated_section_to_segment): If making shared
	library, put .interp section in PT_INTERP segment.
	(Layout::finalize): Also call create_interp if -dynamic-linker
	option was used.
	(Layout::create_interp): Assert that there is no PT_INTERP
	segment.  If not using a SECTIONS clause, use make_output_section.
	(Layout::make_output_segment): Set interp_segment_ if PT_INTERP.
	* script-sections.cc
	(Script_sections::create_note_and_tls_segments): If making shared
	library, put .interp section in PT_INTERP segment.