[tlbuild] PPC builds

[Johannes Hielscher]

> If you believe the number of such users is bigger than one, you could
> probably talk to Karl about providing official binaries yourself (but
> then at least make sure that those binaries work on Debian 8).

I did have a Debian Jessie installation, so I had to try. The new clisp
fails to build with some strange memory allocation error. But the TL
build itself worked (without xindy; I still didn't try asy).
So, I could provide at least those 431 binaries for TL18/powerpc-linux.
Exhume the recently buried?