ci: hook up scan-build in the analysis stage
Wrap the default ninja scan-build
with a wrapper that generates plist files
as output - we can then parse those files and produce JUnit-compatible XML.
This can be handled by gitlab's CI so any scan-build failures show up as test
results in the MR UI.
This should show "Test summary contained 272 failed out of 272 total tests" and pressing on "Expand" shows (a subset) of the various bugs. The script adds a bit of context so we don't have to go digging into the scan-build output for every issue.
Note that it's allowed to fail because, well, we currently have 272 errors and that'll take a while to fix.