Fix left shift overflow UB in PPC backend on LLP64 platforms

Author: rnk

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -9189,7 +9189,7 @@ static SDValue getCanonicalConstSplat(uint64_t Val, unsigned SplatSize, EVT VT,
   EVT ReqVT = VT != MVT::Other ? VT : VTys[SplatSize-1];
 
   // For a splat with all ones, turn it to vspltisb 0xFF to canonicalize.
-  if (Val == ((1LU << (SplatSize * 8)) - 1)) {
+  if (Val == ((1LLU << (SplatSize * 8)) - 1)) {
     SplatSize = 1;
     Val = 0xFF;
   }