Generate BFD_RELOC_MMIX_PUSHJ_STUBBABLE for PUSHJ when possible.

	Generate BFD_RELOC_MMIX_PUSHJ_STUBBABLE for PUSHJ when possible.
	* doc/c-mmix.texi (MMIX-Opts): Document --no-pushj-stubs and
	--no-stubs.
	* config/tc-mmix.c: Include limits.h.  Expand on mmix_relax_table
	comment.
	(expand_op, mmix_next_semicolon_is_eoln): Fix head comment.
	(pushj_stubs): New variable.
	(OPTION_NOPUSHJSTUBS, STATE_PUSHJSTUB, PUSHJSTUB_MIN)
	(PUSHJSTUB_MAX): New macros.
	(md_longopts): New options "--no-pushj-stubs" and synonym
	"--no-stubs".
	(mmix_relax_table): Handle new entry for STATE_PUSHJSTUB.
	(md_parse_option): Handle OPTION_NOPUSHJSTUBS.
	(md_estimate_size_before_relax): Modify STATE_PUSHJ state for
	PUSHJ stub relaxation.
	(md_convert_frag): Handle STATE_PUSHJSTUB.
	(md_apply_fix3): Handle BFD_RELOC_MMIX_PUSHJ_STUBBABLE.
	(tc_gen_reloc): Ditto.
	(mmix_md_relax_frag): Handle PUSHJ stub relaxation.
	* config/tc-mmix.h (TC_SEGMENT_INFO_TYPE): Define.
	(struct mmix_segment_info_type): New.