[llvm] [SLP] Increase UsesLimit to 64 (PR #99467)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

I've created a branch (perf/slp_usecase_limit) to determine the effect on compile time - it should appear on https://llvm-compile-time-tracker.com/?config=Overview&stat=instructions%3Au&remote=RKSimon in the next hour

https://github.com/llvm/llvm-project/pull/99467