Build errors are not valid red runs in red/green test proofs

When proving a fix with red/green runs (the test fails on the old commit and passes on the fix), check that the new test file compiles against each pre-fix commit. If the test calls a function signature that changed in the fix (e.g. a helper whose parameters were renamed), the old-commit run fails at build time, and that failure says nothing about the bug. Skip those commits or backport a shim, and keep the result of each run (with xcodebuild: -resultBundlePath per label) so a reviewer can tell a TEST failure from a BUILD failure.