[AST] NFC: Fix -Wdeprecated-copy warning

Author: davezarzycki

include/swift/AST/AnyRequest.h

@@ -145,6 +145,10 @@ class AnyRequestBase {
   AnyRequestBase(const AnyRequestBase &other) {
     vtableAndKind = other.vtableAndKind;
   }
+  AnyRequestBase &operator=(const AnyRequestBase &other) {
+    vtableAndKind = other.vtableAndKind;
+    return *this;
+  }
 
 private:
   Derived &asDerived() {