[doc PATCH] mention interaction with noinline in flatten

[Sandra Loosemore]

On 10/11/2018 02:58 PM, Martin Sebor wrote:
> While writing tests for attribute flatten I wasn't 100% sure
> from reading the manual if it would respect attribute noinline
> or if it would override it.  Turns out it's the former so
> the attached patch mentions it in the manual.  Unless there
> are objections I will commit the change tomorrow.

I've been behind on doc patch review, but for the record, this is fine 
with me.

-Sandra