[PATCH][gas][arm] Add -mwarn-restrict-it

[Wilco Dijkstra]

Hi Christophe,

> So default effect of this patch is that the warning will not be
> emitted anymore, unless the user requests it explicitly.

Exactly, most people just find it annoying.

> What is the actual performance impact of these instructions? I mean:
> with your patch most people won't be aware of a possible future
> problem with their code.

Well you get much better performance when you use these instructions
(https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00399.html).

I don't believe it's the assembler's job to warn about potentially slow code.

Cheers,
Wilco