Fix win32 build.

runtime/vm/assembler.cc

Index: runtime/vm/assembler.cc
===================================================================
--- runtime/vm/assembler.cc	(revision 2206)
+++ runtime/vm/assembler.cc	(working copy)
@@ -6,6 +6,7 @@
 #include "vm/cpu.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
+#include "vm/os.h"
 #include "vm/utils.h"
 #include "vm/zone.h"
 
@@ -154,27 +155,27 @@
 // Shared macros are implemented here.
 void Assembler::Unimplemented(const char* message) {
   const char* format = "Unimplemented: %s";
-  const intptr_t len = snprintf(NULL, 0, format, message);
+  const intptr_t len = OS::SNPrint(NULL, 0, format, message);
   char* buffer = reinterpret_cast<char*>(malloc(len + 1));
-  snprintf(buffer, len + 1, format, message);
+  OS::SNPrint(buffer, len + 1, format, message);
   Stop(buffer);
 }
 
 
 void Assembler::Untested(const char* message) {
   const char* format = "Untested: %s";
-  const intptr_t len = snprintf(NULL, 0, format, message);
+  const intptr_t len = OS::SNPrint(NULL, 0, format, message);
   char* buffer = reinterpret_cast<char*>(malloc(len + 1));
-  snprintf(buffer, len + 1, format, message);
+  OS::SNPrint(buffer, len + 1, format, message);
   Stop(buffer);
 }
 
 
 void Assembler::Unreachable(const char* message) {
   const char* format = "Unreachable: %s";
-  const intptr_t len = snprintf(NULL, 0, format, message);
+  const intptr_t len = OS::SNPrint(NULL, 0, format, message);
   char* buffer = reinterpret_cast<char*>(malloc(len + 1));
-  snprintf(buffer, len + 1, format, message);
+  OS::SNPrint(buffer, len + 1, format, message);
   Stop(buffer);
 }