[llvm] Add benchmark scripts for lit performance measurement (PR #197347)

[Paul Kirth via llvm-commits]

================

----------------
ilovepi wrote:

If you need to check these a lot, maybe a`Platform` object that provides APIs for these would be more useful? You only use these in 2 places right now, so instead of SYSTEM, you could just `import system from platform`, and use `system()` over the global variable.

The usage of the `IS_LINUX`, etc is very limited, so you could just as easily use a dictionary or matching statement.

https://github.com/llvm/llvm-project/pull/197347