Work around GCC 10 warning regression in string/tester.c

[Florian Weimer]

* Jeff Law:

> On 10/2/19 6:41 AM, Florian Weimer wrote:
>> * Joseph Myers:
>> 
>>> Any comments on either the patch itself or the principle of working
>>> around such issues in glibc to allow more effective testing if not
>>> fixed quickly in GCC?
>> 
>> I think we should disable those middle-end warnings for the entire file
>> altogether.
> When y'all figure out how you want to do this, can you please pull the
> fix into Fedora?  I was running the Fedora tester using the latest gcc
> snapshot:
>
>> BUILDSTDERR: tester.c: In function 'test_strncat':
>> BUILDSTDERR: tester.c:395:10: error: 'strncat' forming offset [50, 98] is out of the bounds [0, 50] of object 'one' with type 'char[50]' [-Werror=array-bounds]
>> BUILDSTDERR:   395 |   (void) strncat (one, two, 99);
>> BUILDSTDERR:       |          ^~~~~~~~~~~~~~~~~~~~~~
>> BUILDSTDERR: tester.c:61:6: note: 'one' declared here
>> BUILDSTDERR:    61 | char one[50];
>> BUILDSTDERR:       |      ^~~
>
> So this going to affect Fedora when gcc-10 drops in.

Sure, we pull current upstream master into Fedora once per week.

Thanks,
Florian