[llvm] [FileCheck] Limit quadratic partial-match search behavior (PR #147833)

[via llvm-commits]

dyung wrote:

> Reverted in [108023b](https://github.com/llvm/llvm-project/commit/108023b7b16297291553650ea6aea809bd7eb78b), and re-applied in [9a12037](https://github.com/llvm/llvm-project/commit/9a12037c573e884b8f027654b56a6151bd5c0a56)

Just wanted to say the reapplication seems to be working, so that is good for now.

https://github.com/llvm/llvm-project/pull/147833