* as.c (show_usage): Remove target specific messages;

	* as.c (show_usage): Remove target specific messages;
	instead, call md_show_usage.
	(parse_args): Use getopt_long_only.  Take pointers to argc and
	argv.
	(main): Pass parse_args pointers.
	* as.h: Remove 3 variables that are redundant with flagseen.
	* as.c, messages.c: Change their users to use flagseen.
	Define getopt stuff.
	* tc.h: Update md_parse_option decl.  Add md_show_usage decl.
	* config/tc-*.c: Add md_shortopts, md_longopts,
	md_longopts_size, md_show_usage.  Change calling convention for
	md_parse_option.  Remove md_parse_long_option.
	* config/tc-ns32k.c: Rename `struct option' to `struct ns32k_option'.
	* config/tc-i386.h: Don't define md_parse_option.