If a pull request fails to build in EWS because the base branch doesn't build, we end up in an infinite retry. Because we don't automatically rebase pull requests, we shouldn't retry if the base commit fails to build.
<rdar://problem/88344438>
Landed 246651@main (r288911)
Pull Request: https://github.com/WebKit/WebKit/pull/116#pullrequestreview-869839439