[PATCH][gas] Implement .cfi_negate_ra_state directive

[Nick Clifton]

Hi Kyrill,

> Tested gas aarch64-none-elf.
> Ok for master and the release branches?

Approved - please apply.

I do wonder though whether there would be a need
to add other architecture specific extensions like
this in the future ?  If so then it would be better
to define a new target macro which could provide
additions to the cfi_pseudo_table.  A problem for
the future I guess.

Cheers
  Nick