[patch v2] malloc: avoid need for tcache == NULL checks

[Florian Weimer]

* Wilco Dijkstra:

> Hi DJ,
>
>>> I suppose these could be inline functions instead of macros.
>>
>> That's been suggested in the past, and IIRC my reply was "why?"
>> Changing these to functions just makes the file longer, it doesn't
>> change the generated code.  And, I like having all the related macros
>> together like that instead of spread across multiple pages.
>
> The main advantage is that one can add checks in inline functions or make
> changes without ending up with complex multi-line macros.

It also makes it clear there is funny control flow, or access to local
variables.  Some of the existing malloc-internal macros are like that.

Thanks,
Florian