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.