graphics/mesa: Update to 22.3

Release notes: https://lists.freedesktop.org/archives/mesa-announce/2022-November/000695.html
On top of the release notes it seems that Gallium XVMC is also removed, see
https://gitlab.freedesktop.org/mesa/mesa/-/commit/8cc766d8f7eac26b7c029a2fac1bdfdba4776c29 for
more info.
Bump LLVM_DEFAULT to llvm15 so LTO works.
Also update libclc to track the one from llvm15.

Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D37580