FYI: Version number change

FYI, I am going to change the Clang version number to match whatever
the current LLVM version is. This seems to match what we have decided
to call the versions of Clang that go out with LLVM releases.

Previously, we had been setting the Clang version number to be
whatever Apple's Clang product version was, but it makes more sense
for the repo to be tied to the LLVM version by default, and have
vendors who want to brand their own Clang do that in their own build
system.

- Daniel

Sounds great, thanks Daniel,

-Chris