[llvm] use EXPENSIVE_CHECKS macro to enable MF.verify from PPCMIPeephole pass (PR #108075)

[zhijian lin via llvm-commits]

diggerlin wrote:

since using ` EXPENSIVE_CHECKS` can cause a extremely long testing time for llvm-lit , I closed the issue, We will find a better solution later on.

https://github.com/llvm/llvm-project/pull/108075