Fix Windows build by using OS::StrNCpy....

test/cctest/test-debug.cc

Index: test/cctest/test-debug.cc
===================================================================
--- test/cctest/test-debug.cc	(revision 3640)
+++ test/cctest/test-debug.cc	(working copy)
@@ -2202,7 +2202,8 @@
   if (pos == NULL) {
     return false;
   }
-  strncpy(buffer, pos, buffer_size);
+  Vector<char> buf(buffer, buffer_size);
+  OS::StrNCpy(buf, pos, buffer_size);
   buffer[buffer_size - 1] = '\0';
   return true;
 }