[Clang] Avoid some copies in ClangAttrEmitter. NFC. (#193928)

Fixes #94372

clang/utils/TableGen/ClangAttrEmitter.cpp

diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
index ab7dab7..7df99d3 100644
--- a/clang/utils/TableGen/ClangAttrEmitter.cpp
+++ b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -415,9 +415,9 @@
     int64_t Default;
 
   public:
-    DefaultSimpleArgument(const Record &Arg, StringRef Attr,
-                          std::string T, int64_t Default)
-      : SimpleArgument(Arg, Attr, T), Default(Default) {}
+    DefaultSimpleArgument(const Record &Arg, StringRef Attr, std::string T,
+                          int64_t Default)
+        : SimpleArgument(Arg, Attr, std::move(T)), Default(Default) {}
 
     void writeAccessors(raw_ostream &OS) const override {
       SimpleArgument::writeAccessors(OS);
@@ -5332,7 +5332,7 @@
     return Spellings[(size_t)K];
   }
 
-  void add(const Record &Attr, FlattenedSpelling Spelling) {
+  void add(const Record &Attr, const FlattenedSpelling &Spelling) {
     SpellingKind Kind =
         StringSwitch<SpellingKind>(Spelling.variety())
             .Case("GNU", SpellingKind::GNU)