As LLVM is going to release 3.3 soon, its development is put onto
the release_33 branch. This makes the git target check out this
branch instead of master.

Also use the LLVM version variable instead of using the static
version everywhere.

sync distinfo and plist while we're there.
Add llvm 3.4, now that 3.3 nearly is released.
Add a patch for LLVM from OpenBSD which enables libobjc2 to find
LLVM-Config.cmake in its configure stage.
Update LLVM 3.4 PLIST.
To be able to use c11 standard atomics on arm, we need to tell llvm
whether or not we have the atomic operations ldrex/strex.

By defining the the atomic inline width to 64, we allow llvm to
use 64-bit wide ldrex/strex instructions on arm. Those only work
on newer arm cores.

In llvm-3.3 a new check was implemented, which does check which
arm core is supported more precisely. It's only enabled for Linux,
so change it to count us in, too.