libport: Fix build on PowerPC

[Grazvydas Ignotas]

On Tue, May 26, 2015 at 11:16 PM, André Hentschel <nerv at dawncrow.de> wrote:
> It was broken by recent commits
> ---
>  libs/port/interlocked.c | 15 +++++++++++++++

Maybe we could just drop all this powerpc specific code, especially
considering missing cmpxchg64 implementation (better use mutex
fallback there) and that some other platforms (ARM/ARM64) don't have
any of this anyway and just use the fallbacks.

Gražvydas