smlrcc: support archives, improvements

- smlrcc can now compile directly to archives using the '-c -o
archive_name.a' options (it checks the extension of the file in the '-o'
option). A new archive is always created. There are no separate options
to update files in an existing archive or include additional files in an
existing archive.

- link the standard library last (was first)

- forward these compiler options to the compiler: '-signed-char',
'-unsigned-char', '-leading-underscore', '-no-leading-underscore'