swift234

[Driver] Make sure to rebuild dependents when a dirty file fails. (#3935)

Otherwise we get into a situation like this:

1. Change made to the interface of file A.swift that also causes an
   error in A.swift.
2. Fixing the error in A.swift does not affect A.swift's interface.
3. File B.swift that depends on A.swift is not rebuilt, since the most
   recent change to A.swift did not change its interface.

To fix this, mark downstream files as needing to be rebuilt even when
a compilation job fails with errors. Additionally, attempt to be extra
conservative when there's a crash.

rdar://problem/25405605