[llvm] [LoopUnroll] Introduce PragmaUnrollFullMaxIterations as a hard cap on how many iterations we try to unroll (PR #78648)

[via llvm-commits]

modiking wrote:

Gotcha, that seems to be the issue then.

To me this seems like it's a source side fix to ensure full unrolling via specifying the trip count or using `#pragma clang loop unroll(full)`. cc @nikic 

https://github.com/llvm/llvm-project/pull/78648