fix string lifetime issue

Author: farzonl

llvm/include/llvm/IR/DiagnosticInfo.h

@@ -139,7 +139,7 @@ class DiagnosticInfo {
 using DiagnosticHandlerFunction = std::function<void(const DiagnosticInfo &)>;
 
 class DiagnosticInfoGeneric : public DiagnosticInfo {
-  const Twine &MsgStr;
+  const Twine MsgStr;
   const Instruction *Inst = nullptr;
 
 public:

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -759,8 +759,7 @@ class OpLowerer {
         std::string Msg =
             formatv("Unsupported intrinsic {0} for DXIL lowering", F.getName())
                 .str();
-        DiagnosticInfoGeneric Diag(Msg);
-        M.getContext().diagnose(Diag);
+        M.getContext().emitError(Msg);
         HasErrors |= true;
         break;
       }