[llvm] [DA] add debug log in ExactRDIVtest (PR #189537)

[Ruoyu Qiu via llvm-commits]

cabbaken wrote:

>  // find gcd
  APInt G, X, Y;
  APInt AM = ConstSrcCoeff->getAPInt();
  APInt BM = ConstDstCoeff->getAPInt();
  APInt CM = ConstDelta->getAPInt();

`CM` is `Delta`. It may not be necessary to add this log, I just want to align `AM` and `BM`, providing more info.

https://github.com/llvm/llvm-project/pull/189537