Among other things, this gets us GCC 10 (was 6).
Requires some changes to third party components we use:
* Install apitrace (& waffle) from Debian; was hitting issues with the
local build, and it's the same version 9.0 anyway.
* Update Fossilize to a newer commit which builds with GCC 10.
* apt.llvm.org repositories are no longer needed.
* Use an SPIRV-LLVM-Translator commit which builds with LLVM 11.0.1.
* Install XCB packages from Debian, 1.13 fails to build with Python 3.9.
* Install wayland-protocols from Debian, 1.12 is too old for
libgtk-3-dev in bullseye.
LLVM 7/8 packages are no longer available.
Also adapt expected test results to Xvfb now exposing multi-samle
GLXFBConfigs.
v2:
* Install clang instead of clang-11.
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3124
Reviewed-by: Eric Anholt <eric@anholt.net> # v1
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9833>
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