[PATCH v2] NEWS: Add entry for x86-64 ISA level build

[Joseph Myers]

On Wed, 27 Jul 2022, Noah Goldstein via Libc-alpha wrote:

> +* Support building x86-64 with multiple ISA levels has been added.
> +  Higher ISA levels will use better optimized functions in the dynamic
> +  loader and non-multiarch build as well as reduce the size of libc.so.

I don't think "with multiple ISA levels" is very meaningful to users.  
How is "with multiple ISA levels" different from the multi-arch feature 
that's been present for many years - I think it could easily be read as a 
description of that longstanding existing feature?  You need a description 
that makes clear to users who aren't following glibc development what the 
actual new feature is (i.e. that if you build with a compiler that 
defaults to a newer ISA level such as -march=x86-64-v2, the resulting libc 
will use corresponding optimized implementations and omit the versions 
only relevant on older processors, if I'm understanding the feature 
correctly).

-- 
Joseph S. Myers
joseph@codesourcery.com