[compiler-rt] [sanitizer] Add type __sanitizer::ssize (PR #116957)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

I landed part as 9a156f6, and undone 04d2450, because internal_strlen is not changed anyway.
Feel free to send another PR if you think it worth it.

https://github.com/llvm/llvm-project/pull/116957