devel/llvm17: Update to 17.0.0rc2

For changes see:
https://discourse.llvm.org/t/llvm-17-0-0-rc2-released/72658

COMPILER_RT is currently disabled for aarch64 as it is broken due to
https://github.com/llvm/llvm-project/issues/63418. Hopefully a fix will
be found before the full release or I'll attempt use a smaller hammer
that only disables ubsan.