I can't bisect a problem in Cairo's test suite because I can't find an old revision that passes the test.
It *could* have been due to changes in pixman, but that code in pixman hasn't changed in the amount of time since the oldest revision in Cairo that I'm looking at.
Of course with plain pkg-config dependencies, there's no way to tie a git revision to the actual version of the dependency that it was tested with.
I.e. if there was Cargo.lock for C, this would be a lot easier.