[Lit] Sort previously failed tests early

D98179 added a mechanism to sort tests by test time to run slow tests
early, increasing potential parallelism. It also added a feature where
negative tests would be marked as negative, allowing subsequent test
runs to run them earlier. Unfortunately it never actually stored the
negative time, even if all the other code seemed to be inplace to sort
them early. Luckily the fix seems simple.

Differential Revision: https://reviews.llvm.org/D130570