[libc-coord] Add new ABI '__memcmpeq()' to libc

[Joseph Myers]

On Thu, 16 Sep 2021, Chris Kennelly wrote:

> In terms of relying on the feature:  If __memcmpeq is ever exposed as an a
> simple alias for memcmp (since the notes mention that it's a valid
> implementation), does that open up the possibility of depending on the
> bcmp-like behavior that we were trying to escape?

The proposal is as an ABI only (compilers would generate calls to 
__memcmpeq from boolean uses of memcmp, users wouldn't write calls to 
__memcmpeq directly, __memcmpeq wouldn't be declared in installed libc 
headers).  If such dependence arises, that would suggest a compiler bug 
wrongly generating such calls for non-boolean memcmp uses.

-- 
Joseph S. Myers
joseph@codesourcery.com