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

[James Henderson via llvm-commits]

jh7370 wrote:

Am I right in thinking this unconditionally truncates the output? What happens if the interesting bit of the output is in the truncated portion? I think at the very least there needs to be an ability to override the truncation. There's nothing more frustrating than finding tools truncating information without an option to see the full set ([I'm looking at you GitHub](https://github.com/llvm/llvm-project/tree/main/lld/test/ELF)...). 

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