bfd/mmo.c: handle "objcopy --extract-symbols" generating and reading back.

bfd/mmo.c: handle "objcopy --extract-symbols" generating and reading back.

bfd:
	* mmo.c (struct mmo_data_struct): New members
	symbol_consistency_override_calculated and ignore_symbol_consistency.
	(mmo_section_has_contents, mmo_ignore_symbol_consistency): New
	functions.
	(mmo_create_symbol): Check with mmo_ignore_symbol_consistency if to
	report an error for unexpected value of Main.
	(mmo_write_symbols_and_terminator): Similar.