[PATCH][GAS] aarch64: Add +pauth flag for Pointer Authentication feature

[Przemyslaw Wirkus]

> > OK for master ?
> 
> I think that you also need to update gas/doc/c-aarch64.texi to include a
> mention of this new extension option.  Approved with that change.

Thank you for pointing that out. I've updated docs for other feature flags
as well.

commit 3f4ff0886feae9e725ff7c244dbe8dffdb260708

> > gas/ChangeLog:
> >
> > 2020-11-13  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>
> >
> > 	* NEWS: Update news.
> > 	* config/tc-aarch64.c: Add option +pauth to -march.
> > 	* testsuite/gas/aarch64/pac-feat.d: New test.
> > 	* testsuite/gas/aarch64/pac-feat.s: New test.
> >
> 
> Cheers
>    Nick