[ADT] NFC: Fix bogus StringSwitch rule-of-five boilerplate

[davezarzycki]

Summary

Now that 'Str' is constant, the rule-of-five logic needs updating.

[jordan_rose]

That's a source compatibility break, but not one that's likely to matter in practice. LGTM.

[davezarzycki]

Yup. I've already done a ninja check-all with llvm, lld, clang, and clang-tools-extras, and everything seems fine.

[davezarzycki]

This was committed.

include/llvm/ADT/StringSwitch.h

 
 public:
   LLVM_ATTRIBUTE_ALWAYS_INLINE
   explicit StringSwitch(StringRef S)
   : Str(S), Result() { }
 
   // StringSwitch is not copyable.
   StringSwitch(const StringSwitch &) = delete;
+
+  // StringSwitch is not assignable due to 'Str' being 'const'.
   void operator=(const StringSwitch &) = delete;
+  void operator=(StringSwitch &&other) = delete;
 
-  StringSwitch(StringSwitch &&other) {
-    *this = std::move(other);
-  }
-  StringSwitch &operator=(StringSwitch &&other) {
-    Str = std::move(other.Str);
-    Result = std::move(other.Result);
-    return *this;
-  }
+  StringSwitch(StringSwitch &&other)
+    : Str(other.Str), Result(std::move(other.Result)) { }
 
   ~StringSwitch() = default;
 
   // Case-sensitive case matchers
   LLVM_ATTRIBUTE_ALWAYS_INLINE
   StringSwitch &Case(StringLiteral S, T Value) {
     if (!Result && Str == S) {
       Result = std::move(Value);