[llvm] [MachineLICM] Fine tune getRegPressureSetLimit (PR #156173)

[via llvm-commits]

LuoYuanke wrote:

> We really need to get #120690 in to stop recomputing this so many times

Yes, and in #120690 I notice a similar patch has been landed and reverted due to compiling time regression. So I'd like to wait for #120690 being accepted and close the patch.

https://github.com/llvm/llvm-project/pull/156173