[PATCH] Speed up single-threaded case of atomic ops and reduce text size

[Paolo Carlini]

Richard Guenther wrote:

>Uh, do we build with -Wcast-qual?  There's nothing to get this warning
>shut up unfortunately.
>
Yes, but #pragma GCC system_header is missing from this specific file 
(we have it in all the other headers), I think it would do the job, in 
case.

>  But yes, the "real" fix is to get rid of the
>volatile qualifier in the function prototype, but this can't be done
>on v3 due to the ABI issues you mentioned.
>  
>
Indeed, but let's think a bit more about this small change, if we can 
avoid warnings and it's safe wrt those delicate issues, the advantages 
seem worthy for 4.2.x.

Paolo.