[ci] Publish compilation warnings to Code Quality report

In a followup to !261 (merged), I'd like to implement a capture of compilation warnings found during the build stage of the CI. These can then be parsed into a JSON that is added to the Code Quality report which is available in the Pipeline and also in the MR interface. With this, the person reviewing an MR will be able to see compilation warnings either added or removed by the changes. This will be helpful in the big cleanup of compilation warnings and then also in maintaining that cleanliness.