* config/tc-s390.c (s390_arch_size): Initialize to zero.

	* config/tc-s390.c (s390_arch_size): Initialize to zero.
	(current_arch_mask): Rename to current_mode_mask.
	(current_arch_requested): Remove variable.
	(current_cpu): New variable.
	(init_default_arch): Set defaults values for s390_arch_size,
	current_mode_mask and current_cpu.
	(md_parse_option): New options -mesa, -mzarch and -march={g5,g6,z900}.
	(md_begin): Replace current_arch_mask by current_cpu.
	(md_assemble): Adapt check and error message to current_mode_mask and
	current_cpu.