config patch to turn off -Wformat for systems that include it in -Wall

[Paolo Bonzini]

On 03/25/2010 07:55 PM, Mike Stump wrote:
> This patch tuns off -Wformat for systems that include it in -Wall.
> Apple's gcc would be one such system.  On other systems, this
> shouldn't have any effect.  I originally wanted to put this into
> config/mh-darwin, but those flags come before -Wall on the command
> line and hence can't effect it.
>
> Ok?

Ok for 4.5.

Paolo