Documentation for .largecomm and friends

[Nick Clifton]

Hi Jan,

>>   Any objections to this patch for PR 22553 ?
> 
> Sounds plausible, thanks for doing this. What about "and friends"
> though?

The PR also refers to .lbss, .ldata and .lrodata, but I think that
the reporter was mistaken about those.

There is a comment in gas/doc/c-i386.texi mentioning that .code16gcc
is not documented, and a scan of the code indicates that .secrel32,
.operand_check, .sse_check, .disallow_index_reg, and .allow_index_reg
are also missing documentation.

Cheers
  Nick