add back format variadic

Author: vbvictor

clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp

@@ -16,6 +16,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/Support/YAMLParser.h"