[llvm] update_test_checks: keep meta variables stable by default (PR #76748)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

I'm getting back to this now. I've rebased and addressed many of the review comments. I plan to test this a bit more now and perhaps simplify some of the logic around recursion unless I can find a compelling test case that benefits.

https://github.com/llvm/llvm-project/pull/76748