[llvm] [llvm-lit] Ignore malformed `.lit_test_times` entries (PR #191305)

[Jonathan Thackray via llvm-commits]

jthackray wrote:

> That would work. We could also just reraise a custom exception that prints out all the relevant information.

Thanks. I've implemented this as so:
```
fatal: found malformed timing data in '/path/to/.lit_test_times.txt'; remove the file to regenerate it
```
This should avoid the currently ambiguous traceback and provide a clear message about the issue. As to why it happens, I think it's when I interrupt `llvm-lit` midway with `ctrl-c`; it's only occasional, but enough to annoy me (and presumably others too).  

https://github.com/llvm/llvm-project/pull/191305