[llvm] [GISel] Add debug counter to force sdag fallback (PR #78257)

[Amara Emerson via llvm-commits]

aemerson wrote:

Right, it will still work but the debug counter will be a bit misleading if you're expecting a codegen difference between N and N+1 and the N+1th iteration. For that reason I'd recommend putting it just before here in InstructionSelect.cpp:
```
  // Determine if there are any calls in this machine function. Ported from
  // SelectionDAG.
  MachineFrameInfo &MFI = MF.getFrameInfo();
```

https://github.com/llvm/llvm-project/pull/78257