Fix printf formats

src/x87/disasm-x87.cc

Index: src/x87/disasm-x87.cc
diff --git a/src/x87/disasm-x87.cc b/src/x87/disasm-x87.cc
index 91ce2272e9bb33d22dbdcdba91859c9e429d5fd6..e5ae52f4cbd3b9e4e81dd5cf7ca2f99a00b07aa0 100644
--- a/src/x87/disasm-x87.cc
+++ b/src/x87/disasm-x87.cc
@@ -8,6 +8,7 @@
 
 #if V8_TARGET_ARCH_X87
 
+#include "src/base/compiler-specific.h"
 #include "src/disasm.h"
 
 namespace disasm {
@@ -325,8 +326,7 @@ class DisassemblerX87 {
   int FPUInstruction(byte* data);
   int MemoryFPUInstruction(int escape_opcode, int regop, byte* modrm_start);
   int RegisterFPUInstruction(int escape_opcode, byte modrm_byte);
-  void AppendToBuffer(const char* format, ...);
-
+  PRINTF_FORMAT(2, 3) void AppendToBuffer(const char* format, ...);
 
   void UnimplementedInstruction() {
     if (abort_on_unimplemented_) {
@@ -948,7 +948,7 @@ int DisassemblerX87::InstructionDecode(v8::internal::Vector<char> out_buffer,
   const InstructionDesc& idesc = instruction_table_->Get(*data);
   switch (idesc.type) {
     case ZERO_OPERANDS_INSTR:
-      AppendToBuffer(idesc.mnem);
+      AppendToBuffer("%s", idesc.mnem);
       data++;
       break;