llvm: upgrade to 18308e171b5b1dd99627a4d88c7d6c5ff21b8c96 (r445002)

The following packages have been updated:
dev-util/lldb-server
sys-devel/llvm
sys-libs/compiler-rt
sys-libs/libcxx
sys-libs/libcxxabi
sys-libs/llvm-libunwind

BUG=b:213618377
TEST=CQ

Change-Id: I69237191a5211d35ea2517ee6d59a6464637eb4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/3418200
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
19 files changed