PR 10156

	PR 10156
	* layout.cc (Layout::choose_output_section): If we find an
	existing section, update the flags.
	(Layout::create_notes): New function, broken out of
	Layout::finalize.
	(Layout::finalize): Don't create note sections.
	(Layout::create_note): Don't crash if linker script discards
	section.
	(Layout::create_gold_note): Likewise.
	(Layout::create_build_id): Likewise.  Don't set
	after_input_sections on the section.
	(Layout::create_executable_stack_info): Remove target parameter.
	Change caller.
	* layout.h (class Layout): Declare create_notes.  Update
	declaration of create_executable_stack_info.
	* gold.cc (queue_middle_tasks): Call create_notes.
	* output.cc (Output_section::update_flags_for_input_section): Move
	here from output.h.  If SHF_ALLOC flag is newly set, mark address
	invalid.
	* output.h (Output_data::mark_address_invalid): New function.
	(class Output_section): Only declare, not define,
	update_flags_for_input_section.  Remove set_flags.