[patch v4] malloc: avoid need for tcache == NULL checks

[Wilco Dijkstra]

Hi DJ,

>>> ^^^ DJ, I think you should remove that #if.
>>
>> Yup, I had already updated my local copy but was waiting for the rest of
>> the feedback before sending a v5.

Note there are 2 redundant #if USE_TACHE in _int_malloc.

> I still have it on my list to benchmark it, but it's busy before the Cauldron...

So performance of v4 looks good - there are some small differences but
now tcache_free_init uses a tailcall, it works out fine.

Cheers,
Wilco