thoughs on splitting up malloc.c

[Florian Weimer]

* DJ Delorie:

> Thoughts?

If we refactor this, it should be done in such a way that we can
duplicate the frontend code with IFUNCs.  For example, for the initial
libc, we want the tcache to be located in the TCB, but such an
implementation could not be used by secondary libcs.

Thanks,
Florian