[tlbuild] PPC builds

[Karl Berry]

I finally committed this change to kpse-setup.m4 and reautoconfed:

    Date: Sun, 16 Feb 2020 23:09:54 +0100
    From: Johannes Hielscher <jhielscher at posteo.de>

    -                   [... powerpc-*-darwin* ],
    +                   [... powerpc-*-darwin* | powerpc*-*-linux* ],
    ...
    If the wildcard of this patch might be too disruptive wrt other related
    platforms, it might be further specified down to the level of
    > powerpc64le-unknown-linux-gnu

I decided to go the other direction, and just disable jit for any
powerpc-*. In the event that there is ever some powerpc platform that
needs to support jit, we can refine it then.

The other point from that mail, about vsx, I still have to look
at. --best, karl.