Mangle.cpp - fix implicit Format.h dependency. NFC.

ProfileSummary was depending on other headers (notably via WithColor.h) to define format().

clang/lib/AST/Mangle.cpp

@@ -25,6 +25,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace clang;