Unbreak clang 19 (compiled by 19) on macppc

clang 19 was miscompiling its own llvm::MergeBasicBlockIntoOnlyPred
(Transform/Utils/Local.cpp).  A change between clang 18 and 19 exposed
a mistake in BitPermutationSelector (PPCISelDAGToDAG.cpp).  It
optimized away a permutation (rotate all 32 bits left by 0) and got
result number 1 from a load pre-inc SDNode, but the node replacement
assumed result number 0.  Kludge by adding an extra node.

llvm/llvm-project#133507
llvm/llvm-project#151429

This isn't the best fix.  I will replace it if LLVM commits a
different fix.

ok miod@

Author: gkoehler

gnu/llvm/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -2337,6 +2337,11 @@ class BitPermutationSelector {
                         ANDIVal, ANDISVal), 0);
     }
 
+    // Caller assumes ResNo == 0, but we might have ResNo != 0 after
+    // optimizing away a permutation.  Kludge with an extra node.
+    if (Res.getResNo() != 0)
+      return CurDAG->getMachineNode(PPC::OR, dl, MVT::i32, Res, Res);
+
     return Res.getNode();
   }