[BACKEND] bump to llvm/llvm-project@ffe3129e9bdc (#5814)

Pulls in llvm/llvm-project#125268 which is
necessary for #5563.

Author: makslevental

cmake/llvm-hash.txt

@@ -1 +1 @@
-c118864223c6309378cd704f3406533474c2759f
+ffe3129e9bdc146ee4d91e849173d1c64b1ae974

lib/Target/LLVMIR/LLVMIRBreakPhiStruct.cpp

@@ -17,7 +17,7 @@ static bool processPhiStruct(PHINode *phiNode) {
   unsigned numOperands = phiNode->getNumIncomingValues();
   unsigned numScalarEl = STy->getNumElements();
   Value *newStruct = UndefValue::get(STy);
-  builder.SetInsertPoint(phiNode->getParent()->getFirstNonPHI());
+  builder.SetInsertPoint(phiNode->getParent()->getFirstNonPHIIt());
   llvm::IRBuilderBase::InsertPoint insertInsertPt = builder.saveIP();
   for (unsigned i = 0; i < numScalarEl; i++) {
     builder.SetInsertPoint(phiNode);