[llvm] [lit] Truncate process output to 10 kiB (PR #206355)

[Nikita Popov via llvm-commits]

nikic wrote:

10KB isn't all that much, esp. if this applies for data piped between processes in the internal shell.

Why does lit send all the output back to the main process?

https://github.com/llvm/llvm-project/pull/206355