The help document of as misses some many options

	PR 29623
	* as.c (show_usage): Document the --dump-config,
	--gdwarf-cie-version, --hash-size, --multibyte-handling,
	and --reduce-memory-overheads options.
	* config/tc-i386.c (md_show_usage): Document the -O option.
	* doc/as.texi: Document the --dump-config, --emulation,
	--hash-size, and --reduce-memory-overheads options.