apt.llvm.org signature has changed, we also should use debian:stable
(=buster) as a base image to correctly install packages.
Removed jdk from the base image as it was used only by Jenkins.
Log packages version for every build.
Related issues: #112
- added simple script to define pipeline, it will check out from this
repo later
- refactored docker container, e.g. merged most of the RUN steps into
one and moved steps that are likely to change closer to the end. That
should improve rebuild / upload speed.
Sample run: https://buildkite.com/llvm-project/premerge/builds/14
