Initialize SaveInfo in methods Output::preflightKey and Output::preflightElement.

[kda]

Summary

When enabling MSAN eager mode with noundef analysis these variables were found to not be initialized in unit tests.

llvm/lib/Support/YAMLTraits.cpp

void Output::endMapping() {
   StateStack.pop_back();
 }
 
 std::vector<StringRef> Output::keys() {
   report_fatal_error("invalid call");
 }
 
 bool Output::preflightKey(const char *Key, bool Required, bool SameAsDefault,
-                          bool &UseDefault, void *&) {
+                          bool &UseDefault, void *&SaveInfo) {
   UseDefault = false;
+  SaveInfo = nullptr;
   if (Required || !SameAsDefault || WriteDefaultValues) {
     auto State = StateStack.back();
     if (State == inFlowMapFirstKey || State == inFlowMapOtherKey) {
       flowKey(Key);
     } else {
       newLineCheck();
       paddedKey(Key);
     }
if (StateStack.back() == inSeqFirstElement) {
     Padding = PaddingBeforeContainer;
     newLineCheck(/*EmptySequence=*/true);
     output("[]");
     Padding = "\n";
   }
   StateStack.pop_back();
 }
 
-bool Output::preflightElement(unsigned, void *&) {
+bool Output::preflightElement(unsigned, void *&SaveInfo) {
+  SaveInfo = nullptr;
   return true;
 }
 
 void Output::postflightElement(void *) {
   if (StateStack.back() == inSeqFirstElement) {
     StateStack.pop_back();
     StateStack.push_back(inSeqOtherElement);
   } else if (StateStack.back() == inFlowSeqFirstElement) {