S390: Silence gcc 5.1 array-bounds warnings if build with -O3.

[Florian Weimer]

On 01/28/2016 09:21 AM, Stefan Liebler wrote:
> The gcc 5.1 reports some "array subscript is above array bounds"
> warnings if compiled with -O3 on s390x. There are no warnings with -O2.
> Older or newer GCCs do not report these warnings.
> 
> This patch silences these warnings with DIAG_* macros,
> except the test-cases, where an assert is included.
> 
> Does anybody see these warnings on other architectures, too?
> Is it okay to silence these warnings?

Do you know if these warnings are related to GCC optimization decisions,
or are just there to educate the programmer?

Florian