Create a libclang package based on the Rust toolchain's LLVM build

for V8 which will use it to inspect C++ object layouts for Torque
(metagen).

Bug: 531344950
Change-Id: Iaf4564f3d8ffacc98509fed8ca945e164ba647af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7992497
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Zequan Wu <zequanwu@google.com>
Cr-Commit-Position: refs/heads/main@{#1657490}
NOKEYCHECK=True
GitOrigin-RevId: e07129e1b252e3e474083ef60120fc09ff80a1fe