PowerPC clang announcement

[Justin Hibbits]

Hello all PowerPC users,

As of r356113 (__FreeBSD_Version 1300070) Clang is now the default
compiler for all PowerPC targets.

At this time, powerpcspe requires extra patches available on
https://reviews.llvm.org/ D69483 and D69484, as well as explicitly
specifying the TARGET_TRIPLE=powerpc-unknown-freebsd13.0 and
LLVM_TARGET_TRIPLE=powerpc-unknown-freebsd13.0.  (I would like to hear
from anyone who *is* using FreeBSD on a powerpcspe platform, off-list).

As mentioned before, the powerpc64 change is also a change to the new
ELFv2 ABI, which is binary incompatible with the previous ABI.
Therefore, it is recommended to perform a complete reinstall of the
system on powerpc64 platforms.

I would like to thank Alfredo Dal'Ava Júnior for all his efforts
getting us to this point, as well as Brandon Bergren on system
and kernel work, and Piotr Kubaj, and Mark Linimon for getting ports
into shape for the transition.  Anyone else I forgot, I do apologize,
this has been a long effort, with many involved.

- Justin