Add attributions so printf like functions can have their arguments checked.

runtime/vm/il_printer.h

Index: runtime/vm/il_printer.h
diff --git a/runtime/vm/il_printer.h b/runtime/vm/il_printer.h
index 347865b613faac358b707ea04bc5eb1cafffa5ed..a6e310c319b9e305f8382809a79a77b52962e30f 100644
--- a/runtime/vm/il_printer.h
+++ b/runtime/vm/il_printer.h
@@ -18,7 +18,7 @@ class BufferFormatter : public ValueObject {
       size_(size) { }
 
   void VPrint(const char* format, va_list args);
-  void Print(const char* format, ...);
+  void Print(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
 
  private:
   intptr_t position_;
@@ -72,7 +72,7 @@ class FlowGraphVisualizer : public ValueObject {
  private:
   // Helpers for printing.
   void PrintInstruction(Instruction* instr);
-  void Print(const char* format, ...);
+  void Print(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
 
   const Function& function_;
   const GrowableArray<BlockEntryInstr*>& block_order_;