Add new linker option: --warn-orphan which generates warning messages when orphan...

Add new linker option: --warn-orphan  which generates warning messages when orphan sections are detected.

ld	* ld.h (struct ld_config_type): Add new field: warn_orphan.
	* ldlex.h (enum option_values): Add OPTION_WARN_ORPHAN and
	OPTION_NO_WARN_ORPHAN.
	* lexsup.c (ld_options): Add --warn-orphan and --no-warn-orphan.
	(parse_args): Handle the new options.
	* ldemul.c (ldemul_place_orphan): If requested, generate a warning
	message when an orphan section is placed in the output file.
	* ld.texinfo: Document the new option.
	* NEWS: Mention the new feature.

tests	* ld-elf/orphan-5.l: New test - checks the linker's output with
	--warn-orphan enabled.
	* ld-elf/elf.exp: Run the new test.