Bump LLVM version to 17.0.6

Changes: https://discourse.llvm.org/t/llvm-17-0-2-released/73840
Changes: https://discourse.llvm.org/t/llvm-17-0-3-released/74172
Changes: https://discourse.llvm.org/t/llvm-17-0-4-released/74548
Changes: https://discourse.llvm.org/t/llvm-17-0-5-released/74906
Changes: https://discourse.llvm.org/t/llvm-17-0-6-released/75281

LLVM 17.0.6 has just been released. For full set of changes in this
release please see the links above. There are no changes in these
releases that are particularly relevant to Xamarin.Android. This is
merely a sync release so that we continue tracking the latest LLVM
stable release in our toolchain.

Author: grendello