[PATCH v2] xmalloc: Fix warnings with gcc analyzer

[Florian Weimer]

* Siddhesh Poyarekar:

> On 7/28/21 4:44 PM, Florian Weimer via Libc-alpha wrote:
>> * Siddhesh Poyarekar:
>> 
>>>   extern void *xrealloc (void *o, size_t n)
>>> +  __attribute_malloc__ __attribute_alloc_size__ ((2)) __attr_dealloc_free
>>> +  __returns_nonnull;
>> Sorry, this one has again __returns_nonnull for xrealloc.
>
> The xrealloc in programs does a malloc(1) if the size requested is 0,
> so it never really returns a NULL.

So it does not free anything ever?

We should not have two different attributes for xrealloc.  I suggest to
drop the attribute from the include/* version for now, until we can
clean this up.

Thanks,
Florian