[clang] [Utils] add update-verify-tests.py (PR #97369)

[Nico Weber via cfe-commits]

nico wrote:

This breaks tests on windows: http://45.33.8.238/win/94083/step_6.txt

Please take a look and revert for now if it takes a while to fix.

https://github.com/llvm/llvm-project/pull/97369