[TableGen] Adapt more places to getValueAsString now returning a StringRef instead of a std::string.

llvm-svn: 304347
diff --git a/llvm/utils/TableGen/SearchableTableEmitter.cpp b/llvm/utils/TableGen/SearchableTableEmitter.cpp
index 80f0b0d..efd4e83 100644
--- a/llvm/utils/TableGen/SearchableTableEmitter.cpp
+++ b/llvm/utils/TableGen/SearchableTableEmitter.cpp
@@ -112,8 +112,8 @@
 void SearchableTableEmitter::emitMappingEnum(std::vector<Record *> &Items,
                                              Record *InstanceClass,
                                              raw_ostream &OS) {
-  std::string EnumNameField = InstanceClass->getValueAsString("EnumNameField");
-  std::string EnumValueField;
+  StringRef EnumNameField = InstanceClass->getValueAsString("EnumNameField");
+  StringRef EnumValueField;
   if (!InstanceClass->isValueUnset("EnumValueField"))
     EnumValueField = InstanceClass->getValueAsString("EnumValueField");