Installing clang-format-11 doesn't seem to work if it's done before
we've installed LLVM. I must admit I didn't try to get to the bottom
of the issue, since installing it after seems to work.
Two problems fixed:
* an old version of clang-format get installed by default (6.0).
* git-clang-format is not present, only git-clang-format-<version> (e.g. git-clang-format-6.0).
Solution:
* install clang-format-11 with explicit version
* make symlink git-clang-format to the latest version of git-clang-format-<version>
Differential Revision: https://reviews.llvm.org/D93201
Remove Phabricator, which isn't needed anymore since we don't report
the job results ourselves. Also, install python3-sphinx instead of
sphinx-doc, since the latter doesn't provide the sphinx-build binary.
This commit adds basic files and scripts that are used for the Buildkite
pre-commit CI setup. This was tested to mostly work on a fork of llvm-project,
however some adjustments will have to be made as we complete the real
setup.